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Deuterium at high-redshift: Primordial abundance in the zabs = 2.621
damped Ly-alpha system towards CTQ247 | The detection of neutral deuterium in the low-metallicity damped
Lyman-{\alpha} system at zabs = 2.621 towards the quasar CTQ247 is reported.
Using a high signal-to-noise and high spectral resolution (R = 60000) spectrum
from the Very Large Telescope Ultraviolet and Visual Echelle Spectrograph, we
precisely measure the deuterium-to-oxygen ratio log N(DI)/N(OI) = 0.74+/-0.04,
as well as the overall oxygen abundance, log N(OI)/N(HI)=-5.29+/-0.10 (or
equivalently [O/H]=-1.99+/-0.10 with respect to the solar value). Assuming
uniform metallicity throughout the system, our measurement translates to (D/H)
= (2.8+0.8 -0.6)x10^-5. This ratio is consistent within errors (<0.4sigma) with
the primordial ratio, (D/H)p = (2.59+/-0.15)x10^-5, predicted by standard
Big-Bang Nucleosynthesis using the WMAP7 value of the cosmological density of
baryons (100 Omega_b h^2 = 2.249+/-0.056). The DI absorption lines are observed
to be broader than the OI absorption lines. From a consistent fit of the
profiles we derive the turbulent broadening to be 5.2 km/s and the temperature
of the gas to be T = 8800+/-1500 K, corresponding to a warm neutral medium.
|
A new catalog of homogenised absorption line indices for Milky Way
globular clusters from high-resolution integrated spectroscopy | We perform integrated spectroscopy of 24 Galactic globular clusters. Spectra
are observed from one core radius for each cluster with a high wavelength
resolution of ~2.0 A FWHM. In combination with two existing data sets from
Puzia et al. (2002) and Schiavon et al. (2005), we construct a large database
of Lick spectral indices for a total of 53 Galactic globular clusters with a
wide range of metallicities, -2.4 < [Fe/H] < 0.1, and various horizontal-branch
morphologies. The empirical index-to-metallicity conversion relationships are
provided for the 20 Lick indices for the use of deriving metallicities for
remote, unresolved stellar systems.
|
Searching for Light Dark Matter with the SLAC Millicharge Experiment | New sub-GeV gauge forces ("dark photons") that kinetically mix with the
photon provide a promising scenario for MeV-GeV dark matter, and are the
subject of a program of searches at fixed-target and collider facilities around
the world. In such models, dark photons produced in collisions may decay
invisibly into dark matter states, thereby evading current searches. We
re-examine results of the SLAC mQ electron beam dump experiment designed to
search for millicharged particles, and find that it was strongly sensitive to
any secondary beam of dark matter produced by electron-nucleus collisions in
the target. The constraints are competitive for dark photon masses in the ~1-30
MeV range, covering part of the parameter space that can reconcile the apparent
(g-2)_{\mu} anomaly. Simple adjustments to the original SLAC search for
millicharges may extend sensitivity to cover a sizable portion of the remaining
(g-2)_{\mu} anomaly-motivated region. The mQ sensitivity is therefore
complementary to on-going searches for visible decays of dark photons. Compared
to existing direct detection searches, mQ sensitivity to electron-dark matter
scattering cross sections is more than an order of magnitude better for a
significant range of masses and couplings in simple models.
|
Exploring interacting holographic dark energy in a perturbed universe
with parameterized post-Friedmann approach | The model of holographic dark energy in which dark energy interacts with dark
matter is investigated in this paper. In particular, we consider the
interacting holographic dark energy model in the context of a perturbed
universe, which was never investigated in the literature. To avoid the
large-scale instability problem in the interacting dark energy cosmology, we
employ the generalized version of the parameterized post-Friedmann approach to
treat the dark energy perturbations in the model. We use the current
observational data to constrain the model. Since the cosmological perturbations
are considered in the model, we can then employ the redshift-space distortions
(RSD) measurements to constrain the model, in addition to the use of the
measurements of expansion history, which was either never done in the
literature. We find that, for both the cases with $Q=\beta H\rho_{\rm c}$ and
$Q=\beta H_0\rho_{\rm c}$, the interacting holographic dark energy model is
more favored by the current data, compared to the holographic dark energy model
without interaction. It is also found that, with the help of the RSD data, a
positive coupling $\beta$ can be detected at the $2.95\sigma$ statistical
significance for the case of $Q=\beta H_0\rho_{\rm c}$.
|
Spinning dust emission from ultrasmall silicates: emissivity and
polarization spectrum | Anomalous microwave emission (AME) is an important Galactic foreground of
Cosmic Microwave Background (CMB) radiation. It is believed that the AME arises
from rotational emission by spinning polycyclic aromatic hydrocarbons (PAHs) in
the interstellar medium (ISM). In this paper, we assume that a population of
ultrasmall silicate grains may exist in the ISM, and quantify rotational
emissivity from these tiny particles and its polarization spectrum. We found
that spinning silicate nanoparticles can produce strong rotational emission
when those small grains follow a log-normal size distribution. The polarization
fraction of spinning dust emission from tiny silicates increases with
decreasing the dipole moment per atom ($\beta$) and can reach $P\sim 20\%$ for
$\beta\sim 0.1$D at grain temperature of 60 K. We identify a parameter space
$(\beta,Y_{Si})$ for silicate nanoparticles in which its rotational emission
can adequately reproduce both the observed AME and the polarization of the AME,
without violating the observational constraints by the ultraviolet extinction
and polarization of starlight. Our results reveal that rotational emission from
spinning silicate may be an important source of the AME.
|
High resolution spectroscopic follow-up of the most metal-poor
candidates from SkyMapper DR1.1 | We present chemical abundances for 21 elements (from Li to Eu) in 150
metal-poor Galactic stars spanning $-$4.1 $<$ [Fe/H] $<$ $-$2.1. The targets
were selected from the SkyMapper survey and include 90 objects with [Fe/H]
$\le$ $-$3 of which some 15 have [Fe/H] $\le$ $-$3.5. When combining the sample
with our previous studies, we find that the metallicity distribution function
has a power-law slope of $\Delta$(log N)/$\Delta$[Fe/H] = 1.51 $\pm$ 0.01 dex
per dex over the range $-$4 $\le$ [Fe/H] $\le$ $-$3. With only seven
carbon-enhanced metal-poor stars in the sample, we again find that the
selection of metal-poor stars based on SkyMapper filters is biased against
highly carbon rich stars for [Fe/H] $>$ $-$3.5. Of the 20 objects for which we
could measure nitrogen, 11 are nitrogen-enhanced metal-poor stars. Within our
sample, the high NEMP fraction (55\% $\pm$ 21\%) is compatible with the upper
range of predicted values (between 12\% and 35\%). The chemical abundance
ratios [X/Fe] versus [Fe/H] exhibit similar trends to previous studies of
metal-poor stars and Galactic chemical evolution models. We report the
discovery of nine new r-I stars, four new r-II stars, one of which is the most
metal-poor known, nine low-$\alpha$ stars with [$\alpha$/Fe] $\le$ 0.15 as well
as one unusual star with [Zn/Fe] = +1.4 and [Sr/Fe] = +1.2 but with normal
[Ba/Fe]. Finally, we combine our sample with literature data to provide the
most extensive view of the early chemical enrichment of the Milky Way Galaxy.
|
The Impact of Starbursts on the Circumgalactic Medium | We present a study exploring the impact of a starburst on the properties of
the surrounding circum-galactic medium (CGM): gas located beyond the galaxy's
stellar body and extending out to the virial radius (200 kpc). We obtained
ultraviolet spectroscopic data from the Cosmic Origin Spectrograph (COS)
probing the CGM of 20 low-redshift foreground galaxies using background QSOs.
Our sample consists of starburst and control galaxies. The latter comprises
normal star-forming and passive galaxies with similar stellar masses and impact
parameters as the starbursts. We used optical spectra from the Sloan Digital
Sky Survey(SDSS) to estimate the properties of the starbursts, inferring
average ages of 200 Myrs and burst fractions involving ~10% of their stellar
mass. The COS data reveal highly ionized gas traced by CIV in 80%(4/5) of the
starburst and in 17%(2/12) of the control sample. The two control galaxies with
CIV absorbers differed from the four starbursts in showing multiple
low-ionization transitions and strong saturated Lyman-alpha lines. They
therefore appear to be physically different systems. We show that the CIV
absorbers in the starburst CGM represent a significant baryon repository. The
high detection rate of this highly ionized material in the starbursts suggests
that starburst-driven winds can affect the CGM out to radii as large as 200
kpc. This is plausible given the inferred properties of the starbursts and the
known properties of starburst-driven winds. This would represent the first
direct observational evidence of local starbursts impacting the bulk of their
gaseous halos, and as such provides new evidence of the importance of this kind
of feedback in the evolution of galaxies.
|
Galactic kinematics and dynamics from RAVE stars | We analyse the kinematics of ~400000 RAVE stars. We split the sample into hot
and cold dwarfs, red-clump and non-clump giants. The kinematics of the clump
giants are consistent with being identical with those of non-clump giants. We
fit Gaussian velocity ellipsoids to the meridional-plane components of velocity
of each star class and give formulae from which the shape and orientation of
the velocity ellipsoid can be determined at any location. The data are
consistent with the giants and the cool dwarfs sharing the same velocity
ellipsoids; sigma_z rises from 21 kms in the plane to sim 55 kms at |z|=2 kpc,
while sigma_r rises from 37 kms to 82 kms. At (R,z) the longest axis of one of
these velocity ellipsoids is inclined to the Galactic plane by an angle ~0.8
arctan(z/R). We use a novel formula to obtain precise fits to the highly
non-Gaussian distributions of v_phi components.
We compare the observed velocity distributions with the predictions of a
dynamical model fitted to the velocities of stars that lie within ~150 pc of
the Sun and star counts towards the Galactic pole. The model accurately
reproduces the non-Gaussian nature of the v_r and v_z distributions and
provides excellent fits to the data for v_z at all locations. The model v_phi
distributions for the cool dwarfs fit the data extremely well, while those for
the hot dwarfs have displacements to low v_phi that grow with |z| from very
small values near the plane. At |z|>0.5 kpc, the theoretical v_phi
distributions for giants show a deficit of stars with large v_phi and the model
v_r distributions are too narrow. Systematically over-estimating distances by
20 per cent introduces asymmetry into the model v_r and v_z distributions near
the plane and but significantly improves the fits to the data at |z|>0.5 kpc.
The quality of the fits lends credence to the assumed, disc-dominated,
gravitational potential.
|
Redshift-space distortions in massive neutrino and evolving dark energy
cosmologies | Large-scale structure surveys in the coming years will measure the
redshift-space power spectrum to unprecedented accuracy, allowing for powerful
new tests of the LambdaCDM picture as well as measurements of particle physics
parameters such as the neutrino masses. We extend the Time-RG perturbative
framework to redshift space, computing the power spectrum P_s(k,mu) in massive
neutrino cosmologies with time-dependent dark energy equations of state w(z).
Time-RG is uniquely capable of incorporating scale-dependent growth into the
P_s(k,mu) computation, which is important for massive neutrinos as well as
modified gravity models. Although changes to w(z) and the neutrino mass
fraction both affect the late-time scale-dependence of the non-linear power
spectrum, we find that the two effects depend differently on the line-of-sight
angle mu. Finally, we use the HACC N-body code to quantify errors in the
perturbative calculations. For a LambdaCDM model at redshift z=1, our procedure
predicts the monopole~(quadrupole) to 1% accuracy up to a wave number 0.19h/Mpc
(0.28h/Mpc), compared to 0.08h/Mpc (0.07h/Mpc) for the Kaiser approximation and
0.19h/Mpc (0.16h/Mpc) for the current state-of-the-art perturbation scheme. Our
calculation agrees with the simulated redshift-space power spectrum even for
neutrino masses above the current bound, and for rapidly-evolving dark energy
equations of state, |dw/dz| ~ 1. Along with this article, we make our
redshift-space Time-RG implementation publicly available as the code redTime.
|
The Chaotic Regime of D-Term Inflation | We consider D-term inflation for small couplings of the inflaton to matter
fields. Standard hybrid inflation then ends at a critical value of the inflaton
field that exceeds the Planck mass. During the subsequent waterfall transition
the inflaton continues its slow-roll motion, whereas the waterfall field
rapidly grows by quantum fluctuations. Beyond the decoherence time, the
waterfall field becomes classical and approaches a time-dependent minimum,
which is determined by the value of the inflaton field and the self-interaction
of the waterfall field. During the final stage of inflation, the effective
inflaton potential is essentially quadratic, which leads to the standard
predictions of chaotic inflation. The model illustrates how the decay of a
false vacuum of GUT-scale energy density can end in a period of `chaotic
inflation'.
|
Globular clusters and supermassive black holes in galaxies: further
analysis and a larger sample | We explore several correlations between various large-scale galaxy
properties, particularly total globular cluster population (N_GCS), the central
black hole mass (M_BH), velocity dispersion (nominally sigma_e), and bulge mass
(M_dyn). Our data sample of 49 galaxies, for which both N_GC and M_BH are
known, is larger than used in previous discussions of these two parameters and
we employ the same sample to explore all pairs of correlations. Further, within
this galaxy sample we investigate the scatter in each quantity, with emphasis
on the range of published values for sigma_e and effective radius (R_e). We
find that these two quantities in particular are difficult to measure
consistently and caution that precise intercomparison of galaxy properties
involving R_e and sigma_e is particularly difficult.
Using both chi^2 and Monte Carlo Markov Chain (MCMC) fitting techniques, we
show that quoted observational uncertainties for all parameters are too small
to represent the true scatter in the data. We find that the correlation between
M_dyn and N_GC is stronger than either the M_BH-sigma_e or M_BH-N_GC relations.
We suggest that this is because both the galaxy bulge population ans N_GC were
fundamentally established at an early epoch during the same series of
star-forming events. By contrast, although the seed for M_BH was likely formed
at a similar epoch, its growth over time is less similar from galaxy to galaxy
and thus less predictable.
|
Real-time detection of an extreme scattering event: constraints on
Galactic plasma lenses | Extreme scattering events (ESEs) are distinctive fluctuations in the
brightness of astronomical radio sources caused by occulting plasma lenses in
the interstellar medium. The inferred plasma pressures of the lenses are $\sim
10^3$ times the ambient pressure, challenging our understanding of gas
conditions in the Milky Way. Using a new survey technique, we have discovered
an ESE while it was in progress. We report radio and optical follow-up
observations. Modelling of the radio data demonstrates that the lensing
structure is a density enhancement and that the lens is diverging, ruling out
one of two competing physical models. Our technique will uncover many more
ESEs, addressing a long-standing mystery of the small-scale gas structure of
the Galaxy.
|
Non-Parametric Cell-Based Photometric Proxies for Galaxy Morphology:
Methodology and Application to the Morphologically-Defined Star Formation --
Stellar Mass Relation of Spiral Galaxies in the Local Universe | (Abridged) We present a non-parametric cell-based method of selecting highly
pure and largely complete samples of spiral galaxies using photometric and
structural parameters as provided by standard photometric pipelines and simple
shape fitting algorithms, demonstrably superior to commonly used proxies.
Furthermore, we find structural parameters derived using passbands longwards of
the $g$ band and linked to older stellar populations, especially the stellar
mass surface density $\mu_*$ and the $r$ band effective radius $r_e$, to
perform at least equally well as parameters more traditionally linked to the
identification of spirals by means of their young stellar populations. In
particular the distinct bimodality in the parameter $\mu_*$, consistent with
expectations of different evolutionary paths for spirals and ellipticals,
represents an often overlooked yet powerful parameter in differentiating
between spiral and non-spiral/elliptical galaxies. We investigate the intrinsic
specific star-formation rate - stellar mass relation ($\psi_* - M_*$) for a
morphologically defined volume limited sample of local universe spiral
galaxies, defined using the cell-based method with an appropriate parameter
combination. The relation is found to be well described by $\psi_* \propto
M_*^{-0.5}$ over the range of $10^{9.5} M_{\odot} \le M_* \le 10^{11}
M_{\odot}$ with a mean interquartile range of $0.4\,$dex. This is somewhat
steeper than previous determinations based on colour-selected samples of
star-forming galaxies, primarily due to the inclusion in the sample of red
quiescent disks.
|
Self-consistent population spectral synthesis with FADO: II. Star
formation history of galaxies in spectral synthesis methods | The field of galaxy evolution will make a great leap forward in the next
decade as a consequence of the huge effort by the scientific community in
multi-object spectroscopic facilities. To maximise the impact of such incoming
data, the analysis methods must also step up, extracting reliable information
from the available spectra. In this paper, we aim to investigate the limits and
the reliability of different spectral synthesis methods in the estimation of
the mean stellar age and metallicity. The main question this work aims to
address is which signal-to-noise ratios (S/N) are needed to reliably determine
the mean stellar age and metallicity from a galaxy spectrum and how this
depends on the tool used to model the spectra. To address this question we
built a set of realistic simulated spectra containing stellar and nebular
emission, reproducing the evolution of a galaxy in two limiting cases: a
constant star formation rate and an exponentially declining star formation. We
degraded the synthetic spectra built from these two star formation histories
(SFHs) to different S/N and analysed them with three widely used spectral
synthesis codes, namely FADO, STECKMAP, and STARLIGHT. For S/N < 5 all three
tools show a large diversity in the results. The FADO and STARLIGHT tools find
median differences in the light-weighted mean stellar age of ~0.1 dex, while
STECKMAP shows a higher value of ~0.2 dex. Detailed investigations of the
best-fit spectrum for galaxies with overestimated mass-weighted quantities
point towards the inability of purely stellar models to fit the observed
spectra around the Balmer jump. Our results imply that when a galaxy enters a
phase of high specific star formation rate the neglect of the nebular continuum
emission in the fitting process has a strong impact on the estimation of its
SFH when purely stellar fitting codes are used, even in presence of high S/N
spectra.
|
Detecting binary neutron star systems with spin in advanced
gravitational-wave detectors | The detection of gravitational waves from binary neutron stars is a major
goal of the gravitational-wave observatories Advanced LIGO and Advanced Virgo.
Previous searches for binary neutron stars with LIGO and Virgo neglected the
component stars' angular momentum (spin). We demonstrate that neglecting spin
in matched-filter searches causes advanced detectors to lose more than 3% of
the possible signal-to-noise ratio for 59% (6%) of sources, assuming that
neutron star dimensionless spins, $c\mathbf{J}/GM^2$, are uniformly distributed
with magnitudes between 0 and 0.4 (0.05) and that the neutron stars have
isotropically distributed spin orientations. We present a new method for
constructing template banks for gravitational wave searches for systems with
spin. We present a new metric in a parameter space in which the template
placement metric is globally flat. This new method can create template banks of
signals with non-zero spins that are (anti-)aligned with the orbital angular
momentum. We show that this search loses more than 3% of the maximium
signal-to-noise for only 9% (0.2%) of BNS sources with dimensionless spins
between 0 and 0.4 (0.05) and isotropic spin orientations. Use of this template
bank will prevent selection bias in gravitational-wave searches and allow a
more accurate exploration of the distribution of spins in binary neutron stars.
|
Simulating the galaxy cluster "El Gordo": gas motion, kinetic
Sunyaev-Zel'dovich signal, and X-ray line features | The massive galaxy cluster "El Gordo" (ACT-CL J0102--4915) is a rare merging
system with a high collision speed suggested by multi-wavelength observations
and the theoretical modeling. Zhang et al. (2015) propose two types of mergers,
a nearly head-on merger and an off-axis merger with a large impact parameter,
to reproduce most of the observational features of the cluster, by using
numerical simulations. The different merger configurations of the two models
result in different gas motion in the simulated clusters. In this paper, we
predict the kinetic Sunyaev-Zel'dovich (kSZ) effect, the relativistic
correction of the thermal Sunyaev-Zel'dovich (tSZ) effect, and the X-ray
spectrum of this cluster, based on the two proposed models. We find that (1)
the amplitudes of the kSZ effect resulting from the two models are both on the
order of $\Delta T/T\sim10^{-5}$; but their morphologies are different, which
trace the different line-of-sight velocity distributions of the systems; (2)
the relativistic correction of the tSZ effect around $240 {\rm\,GHz}$ can be
possibly used to constrain the temperature of the hot electrons heated by the
shocks; and (3) the shift between the X-ray spectral lines emitted from
different regions of the cluster can be significantly different in the two
models. The shift and the line broadening can be up to $\sim 25{\rm\,eV}$ and
$50{\rm\,eV}$, respectively. We expect that future observations of the kSZ
effect and the X-ray spectral lines (e.g., by ALMA, XARM) will provide a strong
constraint on the gas motion and the merger configuration of ACT-CL
J0102--4915.
|
Thermal Pressures in the Interstellar Medium of the Magellanic Clouds | We discuss the thermal pressures ($n_H T$) in predominantly cold, neutral
interstellar gas in the Magellanic Clouds, derived from analyses of the
fine-structure excitation of neutral carbon, as seen in high-resolution
HST/STIS spectra of seven diverse sight lines in the LMC and SMC. Detailed fits
to the line profiles of the absorption from C I, C I*, and C I** yield
consistent column densities for the 3--6 C I multiplets detected in each sight
line. In the LMC and SMC, $N$(C I$_{\rm tot}$) is consistent with Galactic
trends versus $N$(Na I) and $N$(CH), but is slightly lower versus $N$(K I) and
$N$(H$_2$). As for $N$(Na I) and $N$(K I), $N$(C I$_{\rm tot}$) is generally
significantly lower, for a given $N$(H$_{\rm tot}$), in the LMC and
(especially) in the SMC, compared to the local Galactic relationship. For the
LMC and SMC components with well determined column densities for C I, C I*, and
C I**, the derived thermal pressures are typically factors of a few higher than
the values found for most cold, neutral clouds in the Galactic ISM. Such
differences are consistent with the predictions of models for clouds in systems
(like the LMC and SMC) that are characterized by lower metallicities, lower
dust-to-gas ratios, and enhanced radiation fields -- where higher pressures are
required for stable cold, neutral clouds. The pressures may be further enhanced
by energetic activity (e.g., due to stellar winds, star formation, and/or
supernova remnants) in several of the regions probed by these sight lines.
Comparisons are made with the C I observed in some quasar absorption-line
systems.
|
The Search for Dark Matter | The dark matter problem is almost a century old. Since the 1930s evidence has
been growing that our cosmos is dominated by a new form of non-baryonic matter,
that holds galaxies and clusters together and influences cosmic structures up
to the largest observed scales. At the microscopic level, we still do not know
the composition of this dark, or invisible matter, which does not interact
directly with light. The simplest assumption is that it is made of new
particles that interact with gravity and at most weakly with known elementary
particles. I will discuss searches for such new particles, both space- and
Earth-bound including those placed in deep underground laboratories. While a
dark matter particle hasn't been yet identified, even after decades of
concerted efforts, new technological developments and experiments have reached
sensitivities where a discovery might be imminent, albeit certainly not
guaranteed.
|
Faint Quasars Live in the Same Number Density Environments as Lyman
Break Galaxies at z ~ 4 | Characterizing high-z quasar environments is key to understanding the
co-evolution of quasars and the surrounding galaxies. To restrict their global
picture, we statistically examine the g-dropout galaxy overdensity distribution
around 570 faint quasar candidates at z ~ 4, based on the Hyper Suprime-Cam
Subaru Strategic Program survey. We compare the overdensity significances of
g-dropout galaxies around the quasars with those around g-dropout galaxies, and
find no significant difference between their distributions. A total of 4 (22)
out of the 570 faint quasars, 0.7_{-0.4}^{+0.4} (3.9_{-0.8}^{+0.8}) %, are
found to be associated with the > 4 sigma overdense regions within an angular
separation of 1.8 (3.0) arcmin, which is the typical size of protoclusters at
this epoch. This is similar to the fraction of g-dropout galaxies associated
with the > 4 sigma overdense regions. This result is consistent with our
previous work that 1.3_{-0.9}^{+0.9} % and 2.0_{-1.1}^{+1.1} % of luminous
quasars detected in the Sloan Digital Sky Survey exist in the > 4 sigma
overdense regions within 1.8 and 3.0 arcmin separations, respectively.
Therefore, we suggest that the galaxy number densities around quasars are
independent of their luminosity, and most quasars do not preferentially appear
in the richest protocluster regions at z ~ 4. The lack of an apparent positive
correlation between the quasars and the protoclusters implies that: i) the
gas-rich major merger rate is relatively low in the protocluster regions, ii)
most high-z quasars may appear through secular processes, or iii) some
dust-obscured quasars exist in the protocluster regions.
|
Stable counteralignment of a circumbinary disc | In general, when gas accretes on to a supermassive black hole binary it is
likely to have no prior knowledge of the binary angular momentum. Therefore a
circumbinary disc forms with a random inclination angle, theta, to the binary.
It is known that for theta < 90 degrees the disc will coalign wrt the binary.
If theta > 90 degrees the disc wholly counteraligns if it satisfies cos(theta)
< -J_d/2J_b, where J_d and J_b are the magnitudes of the disc and binary
angular momentum vectors respectively. If however theta > 90 degrees and this
criterion is not satisfied the same disc may counteralign its inner regions
and, on longer timescales, coalign its outer regions. I show that for typical
disc parameters, describing an accretion event on to a supermassive black hole
binary, a misaligned circumbinary disc is likely to wholly co-- or
counter--align with the binary plane. This is because the binary angular
momentum dominates the disc angular momentum. However with extreme parameters
(binary mass ratio M_2/M_1 << 1 or binary eccentricity e ~ 1) the same disc may
simultaneously co- and counter-align. It is known that coplanar prograde
circumbinary discs are stable. I show that coplanar retrograde circumbinary
discs are also stable. A chaotic accretion event on to an SMBH binary will
therefore result in a coplanar circumbinary disc that is either prograde or
retrograde with respect to the binary plane.
|
The collisions of high-velocity clouds with the galactic halo | Spiral galaxies are surrounded by a widely distributed hot coronal gas and
seem to be fed by infalling clouds of neutral hydrogen gas with low metallicity
and high velocities. We numerically study plasma waves produced by the
collisions of these high-velocity clouds (HVCs) with the hot halo gas and with
the gaseous disk. In particular, we tackle two problems numerically: 1)
collisions of HVCs with the galactic halo gas and 2) the dispersion relations
to obtain the phase and group velocities of plasma waves from the equations of
plasma motion as well as further important physical characteristics such as
magnetic tension force, gas pressure, etc. The obtained results allow us to
understand the nature of MHD waves produced during the collisions in galactic
media and lead to the suggestion that these waves can heat the ambient halo
gas. These calculations are aiming at leading to a better understanding of
dynamics and interaction of HVCs with the galactic halo and of the importance
of MHD waves as a heating process of the halo gas.
|
The chemical composition of the Orion star-forming region: II. Stars,
gas, and dust: the abundance discrepancy conundrum | We re-examine the recombination/collisional emission line (RL/CEL) nebular
abundance discrepancy problem in the light of recent high-quality abundance
determinations in young stars in the Orion star-forming region.
We re-evaluate the CEL and RL abundances of several elements in the Orion
nebula and estimate the associated uncertainties, taking into account the
uncertainties in the ionization correction factors for unseen ions. We estimate
the amount of oxygen trapped in dust grains for several scenarios of dust
formation. We compare the resulting gas+dust nebular abundances with the
stellar abundances of a sample of 13 B-type stars from the Orion star-forming
region (Ori\,OB1), analyzed in Papers I and III of this series.
We find that the oxygen nebular abundance based on recombination lines agrees
much better with the stellar abundances than the one derived from the
collisionally excited lines. This result calls for further investigation. If
the CEL/RL abundance discrepancy were caused by temperature fluctuations in the
nebula, as argued by some authors, the same kind of discrepancy should be seen
for the other elements, such as C, N and Ne, which is not what we find in the
present study. Another problem is that with the RL abundances, the energy
balance of the Orion nebula is not well understood. We make some suggestions
concerning the next steps to undertake to solve this problem.
|
Limits on Cosmological Birefringence from the Ultraviolet Polarization
of Distant Radio Galaxies | We report on an update of the test on the rotation of the plane of linear
polarization for light traveling over cosmological distances, using a
comparison between the measured direction of the UV polarization in 8 radio
galaxies at z>2 and the direction predicted by the model of scattering of
anisotropic nuclear radiation, which explains the polarization. No rotation is
detected within a few degrees for each galaxy and, if the rotation does not
depend on direction, then the all-sky-average rotation is constrained to be
\theta = -0.8 +/- 2.2. We discuss the relevance of this result for constraining
cosmological birefringence, when this is caused by the interaction with a
cosmological pseudo-scalar field or by the presence of a Cherns-Simons term.
|
Kinematic modelling of the Milky Way using the RAVE and GCS stellar
surveys | We investigate the kinematic parameters of the Milky Way disc using the RAVE
and GCS stellar surveys. We do this by fitting a kinematic model to the data
taking the selection function of the data into account. For stars in the GCS we
use all phase-space coordinates, but for RAVE stars we use only $(l,b,v_{\rm
los})$. Using MCMC technique, we investigate the full posterior distributions
of the parameters given the data. We investigate the `age-velocity dispersion'
relation for the three kinematic components
($\sigma_R,\sigma_{\phi},\sigma_z$), the radial dependence of the velocity
dispersions, the Solar peculiar motion ($U_{\odot},V_{\odot}, W_{\odot} $), the
circular speed $\Theta_0$ at the Sun and the fall of mean azimuthal motion with
height above the mid-plane. We confirm that the Besan\c{c}on-style Gaussian
model accurately fits the GCS data, but fails to match the details of the more
spatially extended RAVE survey. In particular, the Shu distribution function
(DF) handles non-circular orbits more accurately and provides a better fit to
the kinematic data. The Gaussian distribution function not only fits the data
poorly but systematically underestimates the fall of velocity dispersion with
radius. We find that correlations exist between a number of parameters, which
highlights the importance of doing joint fits. The large size of the RAVE
survey, allows us to get precise values for most parameters. However, large
systematic uncertainties remain, especially in $V_{\odot}$ and $\Theta_0$. We
find that, for an extended sample of stars, $\Theta_0$ is underestimated by as
much as $10\%$ if the vertical dependence of the mean azimuthal motion is
neglected. Using a simple model for vertical dependence of kinematics, we find
that it is possible to match the Sgr A* proper motion without any need for
$V_{\odot}$ being larger than that estimated locally by surveys like GCS.
|
Origin of Cosmic Magnetic Fields | We calculate, in the free Maxwell theory, the renormalized quantum vacuum
expectation value of the two-point magnetic correlation function in de Sitter
inflation. We find that quantum magnetic fluctuations remain constant during
inflation instead of being washed out adiabatically, as usually assumed in the
literature. The quantum-to-classical transition of super-Hubble magnetic modes
during inflation, allow us to treat the magnetic field classically after
reheating, when it is coupled to the primeval plasma. The actual magnetic field
is scale independent and has an intensity of few \times 10^(-12) G if the
energy scale of inflation is few \times 10^(16) GeV. Such a field accounts for
galactic and galaxy cluster magnetic fields.
|
Monitoring pulsating giant stars in M33: star formation history and
chemical enrichment | We have conducted a near-infrared monitoring campaign at the UK InfraRed
Telescope (UKIRT), of the Local Group spiral galaxy M 33 (Triangulum). A new
method has been developed by us to use pulsating giant stars to reconstruct the
star formation history of galaxies over cosmological time as well as using them
to map the dust production across their host galaxies. In first Instance the
central square kiloparsec of M33 was monitored and long period variable stars
(LPVs) were identified. We give evidence of two epochs of a star formation rate
enhanced by a factor of a few. These stars are also important dust factories,
we measure their dust production rates from a combination of our data with
Spitzer Space Telescope mid-IR photometry. Then the monitoring survey was
expanded to cover a much larger part of M33 including spiral arms. Here we
present our methodology and describe results for the central square kiloparsec
of M33 (Javadi et al. 2011 a,b,c, 2013) and disc of M33 (Javadi et al. 2015,
2016, 2017, and in preparation).
|
The spatial distribution and origin of the FUV excess in early-type
galaxies | We present surface photometry of a sample of 52 galaxies from the GALEX and
2MASS data archives, these include 32 normal elliptical galaxies, 10
ellipticals with weak Liner or other nuclear activity, and 10 star forming
ellipticals or early-type spirals. We examine the spatial distribution of the
Far Ultra-Violet excess in these galaxies, and its correlation with dynamical
and stellar population properties of the galaxies. From aperture photometry we
find that all galaxies except for recent major remnants and galaxies with
ongoing star formation show a positive gradient in the (FUV-NUV) colour
determined from the GALEX images. The logarithmic gradient does not correlate
with any stellar population parameter, but it does correlate with the central
velocity dispersion. The strength of the excess on the other hand, correlates
with both [alpha/Fe] and [Z/H], but more strongly with the former. We derive
models of the underlying stellar population from the 2MASS H-band images, and
the residual of the image from this model reveals a map of the centrally
concentrated FUV excess. We examine a possible hypothesis for generating the
FUV excess and the radial gradient in its strength, involving a helium
abundance gradient set up early in the formation process of the galaxies. If
this hypothesis is correct, the persistence of the gradients to the present day
places a strong limit on the importance of dry mergers in the formation of
ellipticals.
|
Towards the Future of Supernova Cosmology | For future surveys, spectroscopic follow-up for all supernovae will be
extremely difficult. However, one can use light curve fitters, to obtain the
probability that an object is a Type Ia. One may consider applying a
probability cut to the data, but we show that the resulting non-Ia
contamination can lead to biases in the estimation of cosmological parameters.
A different method, which allows the use of the full dataset and results in
unbiased cosmological parameter estimation, is Bayesian Estimation Applied to
Multiple Species (BEAMS). BEAMS is a Bayesian approach to the problem which
includes the uncertainty in the types in the evaluation of the posterior. Here
we outline the theory of BEAMS and demonstrate its effectiveness using both
simulated datasets and SDSS-II data. We also show that it is possible to use
BEAMS if the data are correlated, by introducing a numerical marginalisation
over the types of the objects. This is largely a pedagogical introduction to
BEAMS with references to the main BEAMS papers.
|
Possible depletion of metals into dust grains in the core of the
Centaurus cluster of galaxies | We present azimuthally averaged metal abundance profiles from a full,
comprehensive, and conservative re-analysis of the deep ($\sim$800 ks total net
exposure) \textit{Chandra}/ACIS-S observation of the Centaurus cluster core
(NGC\,4696). After carefully checking various sources of systematic
uncertainties, including the choice of the spectral deprojection method,
assumptions about the temperature structure of the gas, and uncertainties in
the continuum modeling, we confirm the existence of a central drop in the
abundances of the `reactive' elements Fe, Si, S, Mg, and Ca, within
$r\lesssim$10 kpc. The same drops are also found when analyzing the
\textit{XMM-Newton}/EPIC data ($\sim$150 ks). Adopting our most conservative
approach, we find that, unlike the central drops seen for Fe, Si, S, Mg and Ca,
the abundance of the `nonreactive' element Ar is fully consistent with showing
no central drop. This is further confirmed by the significant ($>3\sigma$)
central radial increase of the Ar/Fe ratio. Our results corroborate the
previously proposed `dust depletion scenario' , in which central metal
abundance drops are explained by the deposition of a significant fraction of
centrally cooled reactive metals into dust grains present in the central
regions of the Centaurus cluster. This is also supported by the previous
findings that the extent of the metal abundance drops in NGC\,4696 broadly
coincides with the infrared dust emission.
|
CMB constraint on non-Gaussianity in isocurvature perturbations | We study the CMB constraint on non-Gaussianity in CDM isocurvature
perturbations. Non-Gaussian isocurvature perturbations can be produced in
various models at the very early stage of the Universe. Since the isocurvature
perturbations little affect the structure formation at late times, CMB is the
best probe of isocurvature non-Gaussianity at least in the near future. In this
paper, we focus on uncorrelated isocurvature perturbations and constrain their
non-Gaussianity. For this purpose, we employ several state-of-art techniques
for the analysis of CMB data and simulation. We use the WMAP 7 year data of
temperature anisotropy. When the adiabatic perturbations are assumed to be
Gaussian, we obtained a constraint on the isocurvature non-Gaussianity alpha^2
f_{NL}^{(ISO)}=40+-66 for the scale invariant isocurvature power spectrum,
where alpha is the ratio of the power spectrum of isocurvature perturbations to
that of the adiabatic ones. When we assume that the adiabatic perturbations can
also be non-Gaussian, we obtain f_{NL}=38+-24 and alpha^2
f_{NL}^{(ISO)}=-8+-72. We also discuss implications our results for the axion
CDM isocurvature model.
|
A Comprehensive Archival Search for Counterparts to Ultra-Compact High
Velocity Clouds: Five Local Volume Dwarf Galaxies | We report five Local Volume dwarf galaxies (two of which are presented here
for the first time) uncovered during a comprehensive archival search for
optical counterparts to ultra-compact high velocity clouds (UCHVCs). The UCHVC
population of HI clouds are thought to be candidate gas-rich, low mass halos at
the edge of the Local Group and beyond, but no comprehensive search for stellar
counterparts to these systems has been presented. Careful visual inspection of
all publicly available optical and ultraviolet imaging at the position of the
UCHVCs revealed six blue, diffuse counterparts with a morphology consistent
with a faint dwarf galaxy beyond the Local Group. Optical spectroscopy of all
six candidate dwarf counterparts show that five have an H$\alpha$-derived
velocity consistent with the coincident HI cloud, confirming their association,
the sixth diffuse counterpart is likely a background object. The size and
luminosity of the UCHVC dwarfs is consistent with other known Local Volume
dwarf irregular galaxies. The gas fraction ($M_{HI}/M_{star}$) of the five
dwarfs are generally consistent with that of dwarf irregular galaxies in the
Local Volume, although ALFALFA-Dw1 (associated with ALFALFA UCHVC
HVC274.68+74.70$-$123) has a very high $M_{HI}/M_{star}$$\sim$40. Despite the
heterogenous nature of our search, we demonstrate that the current dwarf
companions to UCHVCs are at the edge of detectability due to their low surface
brightness, and that deeper searches are likely to find more stellar systems.
If more sensitive searches do not reveal further stellar counterparts to
UCHVCs, then the dearth of such systems around the Local Group may be in
conflict with $\Lambda$CDM simulations.
|
The 6-GHz methanol multibeam maser catalogue IV: Galactic longitudes 186
to 330 including the Orion-Monoceros region | We present the fourth portion of a Galactic Plane survey of methanol masers
at 6668 MHz, spanning the longitude range 186 degrees to 330 degrees. We report
207 maser detections, 89 new to the survey. This completes the southern sky
part of the Methanol Multibeam survey and includes a large proportion of new
sources, 43%. We also include results from blind observations of the
Orion-Monoceros star forming region, formally outside the latitude range of the
Methanol Multibeam survey; only the four previously known methanol emitting
sites were detected, of which we present new positions and spectra for masers
at Orion-A (south) and Orion-B, obtained with the MERLIN array.
|
Matter creation and primordial CMB Spectrum in the inflationless
Milne-like cosmologies | We present a new insight into the interpretation of the primordial spectrum
of scalar particles density perturbations. On the assumption of spectrum
universality, i.e., that the mean energy density and the typical value of
inhomogeneity can be chosen arbitrarily in the framework of the model
considered, the form of the spectrum becomes completely defined. It is close to
the flat Harrison-Zeldovich spectrum, but with the suppressed low-frequency
modes.
|
Detectability of Weak Lensing Modifications under Galileon Theories | Theories of modified gravity attempt to reconcile physics at the largest and
the smallest scales by explaining the accelerated expansion of our universe
without introducing the cosmological constant. One class of such theories,
known as Galileon theories, predict lensing potentials of spherically symmetric
bodies, such as dark matter halos, to receive a feature-like modification at
the 5% level. With the advent of next-generation photometric surveys, such
modifications can serve as novel probes of modified gravity. Assuming an
LSST-like fiducial dataset, we produce halo-shear power spectra for LCDM and
Galileon scenarios, and perform a Fisher analysis including cosmological,
nuisance, and Galileon parameters to study the detectability of the
aforementioned modifications. With the LCDM scenario as our null hypothesis, we
conclude that it is possible to detect the Galileon modifications at up to
4-{\sigma} if present, or strongly exclude the model in a non-detection, with a
tomography of four redshift bins and four mass bins, an LSST-like set of survey
parameters, and Planck priors on cosmological parameters.
|
The Magnification Invariant of Circularly-symmetric Lens Models | In the context of strong gravitational lensing, the magnification of image is
of crucial importance to constrain various lens models. For several commonly
used quadruple lens models, the magnification invariants, defined as the sum of
the signed magnifications of images, have been analytically derived when the
image multiplicity is a maximum. In this paper, we further study the
magnification of several disk lens models, including (a) exponential disk lens,
(b) Gaussian disk lens, (c) modified Hubble profile lens, and another two of
the popular three-dimensional symmetrical lens model, (d) NFW lens and (e)
Einasto lens. We find that magnification invariant does also exist for each
lens model. Moreover, our results show that magnification invariants can be
significantly changed by the characteristic surface mass density $\kappa_{\rm
c}$.
|
Cluster mass dependent truncation of the upper IMF: evidence from
observations and simulations | We attempt to evaluate whether the integrated galactic IMF (IGIMF) is
expected to be steeper than the IMF within individual clusters through direct
evaluation of whether there is a systematic dependence of maximum stellar mass
on cluster mass. We show that the result is sensitive to observational
selection biases and requires an accurate knowledge of cluster ages,
particularly in more populous clusters. At face value there is no compelling
evidence for non-random selection of stellar masses in low mass clusters but
there is arguably some evidence that the maximum stellar mass is anomalously
low (compared with the expectations of random mass selection) in clusters
containing more than several thousand stars. Whether or not this effect is then
imprinted on the IGIMF then depends on the slope of the cluster mass function.
We argue that a more economical approach to the problem would instead involve
direct analysis of the upper IMF in clusters using statistical tests for
truncation of the mass function. When such an approach is applied to data from
hydrodynamic simulations we find evidence for truncated mass functions even in
the case of simulations without feedback.
|
Boxy/Peanut/X-shape bulges: steep inner rotation curve leads to barlens
face-on morphology | We use stellar dynamical bulge/disk/halo simulations to study whether
barlenses (lens-like structures embedded in the narrow bar component) are just
the face-on counterparts of Boxy/Peanut/X-shapes (B/P/X) seen in edge-on bars,
or if some additional physical parameter affects that morphology. A range of
bulge-to-disk mass and size ratios are explored: our nominal parameters
($B/D=0.08$, $r_{\rm eff}/h_r=0.07$, disk comprising 2/3 of total force at
$2.2h_r$) correspond to typical MW mass galaxies. In all models a bar with
pronounced B/P/X forms in a few Gyrs, visible in edge-on view. However, the
pure barlens morphology forms only in models with sufficiently steep inner
rotation curves, $dV_{cir}/dr\gtrsim5V_{max}/h_r$, achieved when including a
small classical bulge with $B/D\gtrsim0.02$ and $r_{\rm eff}/h_r\lesssim0.1$.
For shallower slopes the central structure still resembles a barlens, but shows
a clear X-signature even in low inclinations. Similar result holds for
bulgeless simulations, where the central slope is modified by changing the halo
concentration. The predicted sensitivity on inner rotation curve is consistent
with the slopes estimated from gravitational potentials calculated from the
3.6$\mu$m images, for the observed barlens and X-shape galaxies in the Spitzer
Survey of Stellar Structure in Galaxies (S$^4$G). For inclinations $<60^\circ$
the galaxies with barlenses have on average twice steeper inner rotation curves
than galaxies with X-shapes: the limiting slope is $\sim250$km/s/kpc. Among
barred galaxies, those with barlenses have both the strongest bars and the
largest relative excess of inner surface density, both in barlens region
($\lesssim0.5h_r$) and near the center ($\lesssim0.1h_r$); this provides
evidence for bar-driven secular evolution in galaxies.
|
Are the Carriers of Diffuse Interstellar Bands and Extended Red Emission
the same? | We report the first spectroscopic observations of a background star seen
through the region between the ionization front and the dissociation front of
the nebula IC 63. This photodissociation region (PDR) exhibits intense extended
red emission (ERE) attributed to fluorescence by large molecules/ions. We
detected strong diffuse interstellar bands (DIB) in the stellar spectrum,
including an exceptionally strong and broad DIB at $\lambda$4428. The detection
of strong DIBs in association with ERE could be consistent with the suggestion
that the carriers of DIBs and ERE are identical. The likely ERE process is
recurrent fluorescence, enabled by inverse internal conversions from highly
excited vibrational levels of the ground state to low-lying electronic states
with subsequent transitions to ground. This provides a path to rapid radiative
cooling for molecules/molecular ions, greatly enhancing their ability to
survive in a strongly irradiated environment. The ratio of the equivalent
widths (EW) of DIBs $\lambda$5797 and $\lambda$5780 in IC 63 is the same as
that observed in the low-density interstellar medium with UV interstellar
radiation fields (ISRF) weaker by at least two orders of magnitude. This
falsifies suggestions that the ratio of these two DIBs can serve as a measure
of the UV strength of the ISRF. Observations of the nebular spectrum of the PDR
of IC 63 at locations immediately adjacent to where DIBs were detected failed
to reveal any presence of sharp emission features seen in the spectrum of the
Red Rectangle nebula. This casts doubts upon proposals that the carriers of
these features are the same as those of DIBs seen at slightly shorter
wavelengths.
|
Galaxy bias from forward models: linear and second-order bias of
IllustrisTNG galaxies | We use field-level forward models of galaxy clustering and the EFT likelihood
formalism to study, for the first time for self-consistently simulated
galaxies, the relations between the linear $b_1$ and second-order bias
parameters $b_2$ and $b_{K^2}$. The forward models utilize all of the
information available in the galaxy distribution up to a given order in
perturbation theory, which allows us to infer these bias parameters with high
signal-to-noise, even from relatively small volumes ($L_{\rm box} = 205{\rm
Mpc}/h$). We consider galaxies from the IllustrisTNG simulations, and our main
result is that the $b_2(b_1)$ and $b_{K^2}(b_1)$ relations obtained from
gravity-only simulations for total mass selected objects are broadly preserved
for simulated galaxies selected by stellar mass, star formation rate, color and
black hole accretion rate. We also find good agreement between the bias
relations of the simulated galaxies and a number of recent estimates for
observed galaxy samples. The consistency under different galaxy selection
criteria suggests that theoretical priors on these bias relations may be used
to improve cosmological constraints based on observed galaxy samples. We do
identify some small differences between the bias relations in the
hydrodynamical and gravity-only simulations, which we show can be linked to the
environmental dependence of the relation between galaxy properties and mass. We
also show that the EFT likelihood recovers the value of $\sigma_8$ to
percent-level from various galaxy samples (including splits by color and star
formation rate) and after marginalizing over 8 bias parameters. This
demonstration using simulated galaxies adds to previous works based on halos as
tracers, and strengthens further the potential of forward models to infer
cosmology from galaxy data.
|
A model of nonsingular universe | In the background of Friedmann-Robertson-Walker Universe, there exists
Hawking radiation which comes from the cosmic apparent horizon due to quantum
effect. Although the Hawking radiation on the late time evolution of the
universe could be safely neglected, it plays an important role in the very
early stage of the universe. In view of this point, we identify the temperature
in the scalar field potential with the Hawking temperature of cosmic apparent
horizon. Then we find a nonsingular universe sourced by the
temperature-dependant scalar field. We find that the universe could be created
from a de Sitter phase which has the Planck energy density. Thus the Big-Bang
singularity is avoided.
|
A unified model for the spatial and mass distribution of subhaloes | N-body simulations suggest that the substructures that survive inside dark
matter haloes follow universal distributions in mass and radial number density.
We demonstrate that a simple analytical model can explain these subhalo
distributions as resulting from tidal stripping which increasingly reduces the
mass of subhaloes with decreasing halo-centric distance. As a starting point,
the spatial distribution of subhaloes of any given infall mass is shown to be
largely indistinguishable from the overall mass distribution of the host halo.
Using a physically motivated statistical description of the amount of mass
stripped from individual subhaloes, the model fully describes the joint
distribution of subhaloes in final mass, infall mass and radius. As a result,
it can be used to predict several derived distributions involving combinations
of these quantities including, but not limited to, the universal subhalo mass
function, the subhalo spatial distribution, the gravitational lensing profile,
the dark matter annihilation radiation profile and boost factor. This model
clarifies a common confusion when comparing the spatial distributions of
galaxies and subhaloes, the so called "anti-bias", as a simple selection
effect. We provide a Python code SubGen for populating haloes with subhaloes at
http://icc.dur.ac.uk/data/
|
MSSM inflation, dark matter, and the LHC | Inflation can occur near a point of inflection in the potential of flat
directions of the Minimal Supersymmetric Standard Model. In this paper we
elaborate on the complementarity between the bounds from Cosmic Microwave
Background measurements, dark matter and particle physics phenomenology in
determining the underlying parameters of MSSM inflation by specializing to the
Minimal Supergravity scenario. We show that the future measurements from the
Large Hadron Collider in tandem with all these constraints will significantly
restrict the allowed parameter space. We also suggest a new perspective on the
fine tuning issue of MSSM inflation. With quantum corrections taken into
account, the necessary condition between the soft supersymmetry breaking
parameters in the inflaton potential can be satisfied at scales of interest
without a fine tuning of their boundary values at a high scale. The requirement
that this happens at the inflection point determines a dimensionless coupling,
which is associated with a non-renormalizable interaction term in the
Lagrangian and has no bearing for phenomenology, to very high accuracy.
|
Clearing the hurdle: The mass of globular cluster systems as a function
of host galaxy mass | Current observational evidence suggests that all large galaxies contain
globular clusters (GCs), while the smallest galaxies do not. Over what galaxy
mass range does the transition from GCs to no GCs occur? We investigate this
question using galaxies in the Local Group, nearby dwarf galaxies, and galaxies
in the Virgo Cluster Survey. We consider four types of statistical models: (1)
logistic regression to model the probability that a galaxy of stellar mass
$M_{\star}$ has any number of GCs; (2) Poisson regression to model the number
of GCs versus $M_{\star}$, (3) linear regression to model the relation between
GC system mass ($\log{M_{gcs}}$) and host galaxy mass ($\log{M_{\star}}$), and
(4) a Bayesian lognormal hurdle model of the GC system mass as a function of
galaxy stellar mass for the entire data sample. From the logistic regression,
we find that the 50% probability point for a galaxy to contain GCs is
$M_{\star}=10^{6.8}M_{\odot}$. From post-fit diagnostics, we find that Poisson
regression is an inappropriate description of the data. Ultimately, we find
that the Bayesian lognormal hurdle model, which is able to describe how the
mass of the GC system varies with $M_{\star}$ even in the presence of many
galaxies with no GCs, is the most appropriate model over the range of our data.
In an Appendix, we also present photometry for the little-known GC in the Local
Group dwarf Ursa Major II.
|
Molecules in \eta\ Carinae | We report the detection toward \eta\ Carinae of six new molecules, CO, CN,
HCO+, HCN, HNC, and N2H+, and of two of their less abundant isotopic
counterparts, 13CO and H13CN. The line profiles are moderately broad (about 100
km /s) indicating that the emission originates in the dense, possibly clumpy,
central arcsecond of the Homunculus Nebula. Contrary to previous claims, CO and
HCO+ do not appear to be under-abundant in \eta\ Carinae. On the other hand,
molecules containing nitrogen or the 13C isotope of carbon are overabundant by
about one order of magnitude. This demonstrates that, together with the dust
responsible for the dimming of eta Carinae following the Great Eruption, the
molecules detected here must have formed in situ out of CNO-processed stellar
material.
|
SKA-Low Intensity Mapping Pathfinder Updates: Deeper 21 cm Power
Spectrum Limits from Improved Analysis Frameworks | The Square Kilometre Array (SKA) is a planned radio interferometer of
unprecedented scale that will revolutionize low-frequency radio astronomy when
completed. In particular, one of its core science drivers is the systematic
mapping of the Cosmic Dawn and Epoch of Reionization, which mark the birth of
the first stars and galaxies in the Universe and their subsequent ionization of
primordial intergalactic hydrogen, respectively. The SKA will offer the most
sensitive view of these poorly understood epochs using the redshifted 21 cm
hyperfine signal from intergalactic hydrogen. However, significant technical
challenges stand in the way of realizing this scientific promise. These mainly
involve the mitigation of systematics coming from astrophysical foregrounds,
terrestrial radio interference, and the instrumental response. The Low
Frequency Array, the Murchison Widefield Array and the Hydrogen Epoch of
Reionization Array are SKA pathfinder experiments that have developed a variety
of strategies for addressing these challenges, each with unique characteristics
that stem largely from their different instrumental designs. We outline these
various directions, highlighting key differences and synergies, and discuss how
these relate to the future of low-frequency intensity mapping with the SKA. We
also briefly summarize the challenges associated with modeling the 21 cm signal
and discuss the methodologies being proposed for inferring constraints on
astrophysical models.
|
Gravitational Waves and Dark Radiation from Dark Phase Transition:
Connecting NANOGrav Pulsar Timing Data and Hubble Tension | Recent pulsar timing data reported by the NANOGrav collaboration may indicate
the existence of a stochastic gravitational wave background around $f \sim
10^{-8}$ Hz. We explore a possibility to generate such low-frequency
gravitational waves from a dark sector phase transition. Assuming that the dark
sector is completely decoupled from the visible sector except via the
gravitational interaction, we find that some amount of dark radiation should
remain until present. The NANOGrav data implies that the amount of dark
radiation is close to the current upper bound, which may help mitigate the
so-called Hubble tension. If the existence of dark radiation is not confirmed
in the future CMB-S4 experiment, it would imply the existence of new particles
feebly interacting with the standard model sector at an energy scale of
O(1-100) MeV.
|
Status of CMB observations in 2015 | The 2.725 K cosmic microwave background has played a key role in the
development of modern cosmology by providing a solid observational foundation
for constraining possible theories of what happened at very large redshifts and
theoretical speculation reaching back almost to the would-be big bang initial
singularity. After recounting some of the lesser known history of this area, I
summarize the current observational situation and also discuss some exciting
challenges that lie ahead: the search for B modes, the precision mapping of the
CMB gravitational lensing potential, and the ultra-precise characterization of
the CMB frequency spectrum, which would allow the exploitation of spectral
distortions to probe new physics.
|
Towards conformal cosmology | Approximate de Sitter symmetry of inflating Universe is responsible for the
approximate flatness of the power spectrum of scalar perturbations. However,
this is not the only option. Another symmetry which can explain nearly
scale-invariant power spectrum is conformal invariance. We give a short review
of models based on conformal symmetry which lead to the scale-invariant
spectrum of the scalar perturbations. We discuss also potentially observable
features of these models.
|
A Panchromatic Catalog of Early-Type Galaxies at Intermediate Redshift
in the Hubble Space Telescope Wide Field Camera 3 Early Release Science Field | In the first of a series of forthcoming publications, we present a
panchromatic catalog of 102 visually-selected early-type galaxies (ETGs) from
observations in the Early Release Science (ERS) program with the Wide Field
Camera 3 (WFC3) on the Hubble Space Telescope (HST) of the Great Observatories
Origins Deep Survey-South (GOODS-S) field. Our ETGs span a large redshift
range, 0.35 < z < 1.5, with each redshift spectroscopically-confirmed by
previous published surveys of the ERS field. We combine our measured WFC3 ERS
and ACS GOODS-S photometry to gain continuous sensitivity from the rest-frame
far-UV to near-IR emission for each ETG. The superior spatial resolution of the
HST over this panchromatic baseline allows us to classify the ETGs by their
small-scale internal structures, as well as their local environment. By fitting
stellar population spectral templates to the broad-band photometry of the ETGs,
we determine that the average masses of the ETGs are comparable to the
characteristic stellar mass of massive galaxies, 11< log(M [Solar]) < 12.
By transforming the observed photometry into the GALEX FUV and NUV, Johnson
V, and SDSS g' and r' bandpasses we identify a noteworthy diversity in the
rest-frame UV-optical colors and find the mean rest-frame (FUV-V)=3.5 and
(NUV-V)=3.3, with 1$\sigma$ standard deviations approximately equal to 1.0. The
blue rest-frame UV-optical colors observed for most of the ETGs are evidence
for star-formation during the preceding gigayear, but no systems exhibit
UV-optical photometry consistent with major recent (<~50 Myr) starbursts.
Future publications which address the diversity of stellar populations likely
to be present in these ETGs, and the potential mechanisms by which recent
star-formation episodes are activated, are discussed.
|
Elko under spatial rotations | Under a rotation by an angle $\vartheta$, both the right- and left- handed
Weyl spinors pick up a phase factor ${\exp(\pm\, i \vartheta/2)}$. The upper
sign holds for the positive helicity spinors, while the lower sign for the
negative helicity spinors. For $\vartheta = 2\pi$ radians this produces the
famous minus sign. However, the four-component spinors are built from a direct
sum of the indicated two-component spinors. The effect of the rotation by
$2\pi$ radians on the eigenspinors of the parity - that is, the Dirac spinors
-- is the same as on Weyl spinors. It is because for these spinors the right-
and left- transforming components have the same helicity. And the rotation
induced phases, being same, factor out. But for the eigenspinors of the charge
conjugation operator, i.e. Elko, the left- and right- transforming components
have opposite helicities, and therefore they pick up opposite phases. As a
consequence the behaviour of the eigenspinors of the charge conjugation
operator (Elko) is more subtle: for $0<\vartheta<2\pi$ a self conjugate spinor
becomes a linear combination of the self and antiself conjugate spinors with
$\vartheta$ dependent superposition coefficients - and yet the rotation
preserves the self/antiself conjugacy of these spinors! This apparently
paradoxical situation is fully resolved. This new effect, to the best of our
knowledge, has never been reported before. The purpose of this communication is
to present this result and to correct an interpretational error of a previous
version.
|
21CMMC: an MCMC analysis tool enabling astrophysical parameter studies
of the cosmic 21 cm signal | We introduce 21CMMC: a parallelized, Monte Carlo Markov Chain analysis tool,
incorporating the epoch of reionization (EoR) seminumerical simulation
21CMFAST. 21CMMC estimates astrophysical parameter constraints from 21 cm EoR
experiments, accommodating a variety of EoR models, as well as priors on model
parameters and the reionization history. To illustrate its utility, we consider
two different EoR scenarios, one with a single population of galaxies (with a
mass-independent ionizing efficiency) and a second, more general model with two
different, feedback-regulated populations (each with mass-dependent ionizing
efficiencies). As an example, combining three observations (z=8, 9 and 10) of
the 21 cm power spectrum with a conservative noise estimate and uniform model
priors, we find that interferometers with specifications like the Low Frequency
Array/Hydrogen Epoch of Reionization Array (HERA)/Square Kilometre Array 1
(SKA1) can constrain common reionization parameters: the ionizing efficiency
(or similarly the escape fraction), the mean free path of ionizing photons and
the log of the minimum virial temperature of star-forming haloes to within
45.3/22.0/16.7, 33.5/18.4/17.8 and 6.3/3.3/2.4 per cent, ~$1\sigma$ fractional
uncertainty, respectively. Instead, if we optimistically assume that we can
perfectly characterize the EoR modelling uncertainties, we can improve on these
constraints by up to a factor of ~few. Similarly, the fractional uncertainty on
the average neutral fraction can be constrained to within $\lesssim10$ per cent
for HERA and SKA1. By studying the resulting impact on astrophysical
constraints, 21CMMC can be used to optimize (i) interferometer designs; (ii)
foreground cleaning algorithms; (iii) observing strategies; (iv) alternative
statistics characterizing the 21 cm signal; and (v) synergies with other
observational programs.
|
New Distances to Four Supernova Remnants | Distances are found for four supernova remnants without previous distance
measurements. H I spectra and H I channel maps are used to determine the
maximum velocity of H I absorption for the four supernova remnants (SNRs). We
examined $^{13}$CO emission spectra and channel maps to look for possible
molecular gas associated with each SNR, but did not find any. The resulting
distances for the SNRs are $3.5 \pm 0.2$ kpc (G24.7+0.6), $4.7 \pm 0.3$ kpc
(G29.6+0.1), $4.1 \pm 0.5$ kpc (G41.5+0.4) and $4.5 \pm 0 .4 - 9.0 \pm 0.4$ kpc
(G57.2+0.8).
|
Discovery of Variability in the Very High Energy Gamma-Ray Emission of
1ES 1218+304 with VERITAS | We present results from an intensive VERITAS monitoring campaign of the
high-frequency peaked BL Lac object 1ES 1218+304 in 2008/2009. Although 1ES
1218+304 was detected previously by MAGIC and VERITAS at a persistent level of
~6% of the Crab Nebula flux, the new VERITAS data reveal a prominent flare
reaching ~20% of the Crab. While very high energy (VHE) flares are quite common
in many nearby blazars, the case of 1ES 1218+304 (redshift z = 0.182) is
particularly interesting since it belongs to a group of blazars that exhibit
unusually hard VHE spectra considering their redshifts. When correcting the
measured spectra for absorption by the extragalactic background light, 1ES
1218+304 and a number of other blazars are found to have differential photon
indices less than 1.5. The difficulty in modeling these hard spectral energy
distributions in blazar jets has led to a range of theoretical gamma-ray
emission scenarios, one of which is strongly constrained by these new VERITAS
observations. We consider the implications of the observed light curve of 1ES
1218+304, which shows day scale flux variations, for shock acceleration
scenarios in relativistic jets, and in particular for the viability of
kiloparsec-scale jet emission scenarios.
|
A new scaling relation for HII regions in spiral galaxies: unveiling the
true nature of the mass-metallicity relation | We demonstrate the existence of a -local- relation between galaxy surface
mass density, gas metallicity, and star-formation rate density using
spatially-resolved optical spectroscopy of HII regions in the local Universe.
One of the projections of this distribution, -the local mass-metallicity
relation- extends over three orders of magnitude in galaxy mass density and a
factor of eight in gas metallicity. We explain the new relation as the combined
effect of the differential radial distributions of mass and metallicity in the
discs of galaxies, and a selective star-formation efficiency. We use this local
relation to reproduce -with remarkable agreement- the total mass-metallicity
relation seen in galaxies, and conclude that the latter is a scale-up
integrated effect of a local relation, supporting the inside-out growth and
downsizing scenarios of galaxy evolution.
|
The Photolysis of Aromatic Hydrocarbons Adsorbed on the Surfaces of
Cosmic Dust Grains | The work is devoted to the adaptation of the results of laboratory studies of
the laser-induced dissociation of molecules of benzene adsorbed on a quartz
substrate to the conditions of the interstellar medium. Adsorption was
performed under conditions of low temperature and deep vacuum. The difference
between the photolysis of adsorbed molecules and molecules in the gas phase is
identified. Significance of process of photolytic desorption in the
interstellar conditions is analyzed, in particular, in the conditions of
photodissociation regions. It is shown that the efficiency and dissociation
channels of photolysis of adsorbed and gas phase benzene differ substantially.
It is concluded that the photolysis of aromatic hydrocarbons adsorbed on the
interstellar dust grains contributes a negligible fraction to the abundance of
small hydrocarbons in the interstellar medium.
|
Rubidium in the Interstellar Medium | We present observations of interstellar rubidium toward o Per, zeta Per, AE
Aur, HD 147889, chi Oph, zeta Oph, and 20 Aql. Theory suggests that stable 85Rb
and long-lived 87Rb are produced predominantly by high-mass stars, through a
combination of the weak s- and r-processes. The 85Rb/87Rb ratio was determined
from measurements of the Rb I line at 7800 angstroms and was compared to the
solar system meteoritic ratio of 2.59. Within 1-sigma uncertainties all
directions except HD 147889 have Rb isotope ratios consistent with the solar
system value. The ratio toward HD 147889 is much lower than the meteoritic
value and similar to that toward rho Oph A (Federman et al. 2004); both lines
of sight probe the Rho Ophiuchus Molecular Cloud. The earlier result was
attributed to a deficit of r-processed 85Rb. Our larger sample suggests instead
that 87Rb is enhanced in these two lines of sight. When the total elemental
abundance of Rb is compared to the K elemental abundance, the interstellar Rb/K
ratio is significantly lower than the meteoritic ratio for all the sight lines
in this study. Available interstellar samples for other s- and r- process
elements are used to help interpret these results.
|
Cosmological evolution in Weyl conformal geometry | We discuss the cosmological evolution of the Weyl conformal geometry and its
associated Weyl quadratic gravity. The Einstein gravity (with a positive
cosmological constant) is recovered in the spontaneously broken phase of Weyl
gravity; this happens after the Weyl gauge field ($\omega_\mu$) of scale
symmetry, that is part of the Weyl geometry, becomes massive by Stueckelberg
mechanism and decouples. This breaking is a natural result of the cosmological
evolution of Weyl geometry, in the absence of matter. The Weyl quadratic
gravity provides an accelerated expansion of the Universe controlled by the
scalar mode of the $\tilde R^2$ term in the action and by $\omega_0$. The
comparison to the $\Lambda$CDM model shows a very good agreement between these
two models for the (dimensionless) Hubble function $h(z)$ and the deceleration
$q(z)$ for redshifts $z\leq 3$. Therefore, the Weyl conformal geometry and its
associated Weyl quadratic gravity provide an interesting alternative to the
$\Lambda$CDM model and to the Einstein gravity.
|
Multiple populations along the asymptotic giant branch of the globular
cluster M 4 | Nearly all Galactic globular clusters host stars that display characteristic
abundance anti-correlations, like the O-rich/Na-poor pattern typical of field
halo stars, together with O-poor/Na-rich additional components. A recent
spectroscopic investigation questioned the presence of O-poor/Na-rich stars
amongst a sample of asymptotic giant branch stars in the cluster M 4, at
variance with the spectroscopic detection of a O-poor/Na-rich component along
both the cluster red giant branch and horizontal branch. This is contrary to
what is expected from the cluster horizontal branch morphology and horizontal
branch stellar evolution models. Here we have investigated this issue by
employing the CUBI= (U-B)-(B-I) index, that previous studies have demonstrated
to be very effective in separating multiple populations along both the red
giant and asymptotic giant branch sequences. We confirm previous results that
the RGB is intrinsically broad in the V-CUBI diagram, with the presence of two
components which nicely correspond to the two populations identified by
high-resolution spectroscopy. We find that AGB stars are distributed over a
wide range of CUBI values, in close analogy with what is observed for the RGB,
demonstrating that the AGB of M4 also hosts multiple stellar populations.
|
Signatures of unresolved binaries in stellar spectra: implications for
spectral fitting | The observable spectrum of an unresolved binary star system is a
superposition of two single-star spectra. Even without a detectable velocity
offset between the two stellar components, the combined spectrum of a binary
system is in general different from that of either component, and fitting it
with single-star models may yield inaccurate stellar parameters and abundances.
We perform simple experiments with synthetic spectra to investigate the effect
of unresolved main-sequence binaries on spectral fitting, modeling spectra
similar to those collected by the APOGEE, GALAH, and LAMOST surveys. We find
that fitting unresolved binaries with single-star models introduces systematic
biases in the derived stellar parameters and abundances that are modest but
certainly not negligible, with typical systematic errors of $300\,\rm K$ in
$T_{\rm eff}$, 0.1 dex in $\log g$, and 0.1 dex in $[\rm Fe/H]$ for APOGEE-like
spectra of solar-type stars. These biases are smaller for spectra at optical
wavelengths than in the near-infrared. We show that biases can be corrected by
fitting spectra with a binary model, which adds only two labels to the fit and
includes single-star models as a special case. Our model provides a promising
new method to constrain the Galactic binary population, including systems with
single-epoch spectra and no detectable velocity offset between the two stars.
|
Massive star formation in Wolf-Rayet galaxies: IV b. Using empirical
calibrations to compute the oxygen abundance | We have performed a comprehensive multiwavelength analysis of a sample of 20
starburst galaxies that show a substantial population of very young massive
stars, most of them classified as Wolf-Rayet (WR) galaxies. We have analysed
optical/NIR colours, physical and chemical properties of the ionized gas,
stellar, gas and dust content, star-formation rate and interaction degree
(among many other galaxy properties) of our galaxy sample using
multi-wavelength data. We compile 41 independent star-forming regions --with
oxygen abundances between 12+log(O/H) = 7.58 and 8.75--, of which 31 have a
direct estimate of the electron temperature of the ionized gas. This paper,
only submitted to astro-ph, compiles the most common empirical calibrations to
the oxygen abundance, and presents the comparison between the chemical
abundances derived in these galaxies using the direct method with those
obtained through empirical calibrations, as it is published in Lopez-Sanchez &
Esteban (2010b). We find that (i) the Pilyugin method (Pilyugin 2001a,b;
Pilyugin & Thuan 2005) which considers the R23 and the P parameters, is the
best suited empirical calibration for these star-forming galaxies, (ii) the
relations between the oxygen abundance and the N2 or the O3N2 parameters
provided by Pettini & Pagel (2004) give acceptable results for objects with
12+log(O/H)>8.0, and (iii) the results provided by empirical calibrations based
on photoionization models (McGaugh, 1991; Kewley & Dopita, 2002; Kobulnicky &
Kewley, 2004) are systematically 0.2 -- 0.3 dex higher than the values derived
from the direct method. These differences are of the same order that the
abundance discrepancy found between recombination and collisionally excited
lines. This may suggest the existence of temperature fluctuations in the
ionized gas, as exists in Galactic and other extragalactic HII regions.
|
Fossil stellar streams and their globular cluster populations in the
E-MOSAICS simulations | Stellar haloes encode a fossil record of a galaxy's accretion history,
generally in the form of structures of low surface brightness, such as stellar
streams. While their low surface brightness makes it challenging to determine
their age, metallicity, kinematics and spatial structure, the infalling
galaxies also deposit globular clusters (GCs) in the halo, which are bright and
therefore easier to observe and characterise. To understand how GCs associated
with stellar streams can be used to estimate the stellar mass and the infall
time of their parent galaxy, we examine a subset of 15 simulations of galaxies
and their star clusters from the E-MOSAICS project. E-MOSAICS is a suite of
hydrodynamical simulations incorporating a sub-grid model for GC formation and
evolution. We find that more massive accreted galaxies typically contribute
younger and more metal rich GCs. This lower age results from a more extended
cluster formation history in more massive galaxies. In addition, at fixed
stellar mass, galaxies that are accreted later host younger clusters, because
they can continue to form GCs without being subjected to environmental
influences for longer. This explains the large range of ages observed for
clusters associated with the Sagittarius dwarf galaxy in the halo of the Milky
Way compared to clusters which are thought to have formed in satellites
accreted early in the Milky Way's formation history. Using the ages of the GCs
associated with the Sagittarius dwarf, we estimate a virial radius crossing
lookback time (infall time) of $9.3 \pm 1.8 Gyr$.
|
Giant Clumps in Simulated High-z Galaxies: Properties, Evolution and
Dependence on Feedback | We study the evolution of giant clumps in high-z disc galaxies using AMR
cosmological simulations at redshifts z=6-1. Our sample consists of 34
galaxies, of halo masses 10^{11}-10^{12}M_s at z=2, run with and without
radiation pressure (RP) feedback from young stars. While RP has little effect
on the sizes and global stability of discs, it reduces the amount of
star-forming gas by a factor of ~2, leading to a decrease in stellar mass by a
similar factor by z~2. Both samples undergo violent disc instability (VDI) and
form giant clumps of masses 10^7-10^9M_s at a similar rate, though RP
significantly reduces the number of long-lived clumps. When RP is (not)
included, clumps with circular velocity <40(20)km/s, baryonic surface density
<200(100)M_s/pc^2 and baryonic mass <10^{8.2}(10^{7.3})M_s are short-lived,
disrupted in a few free-fall times. The more massive and dense clumps survive
and migrate toward the disc centre over a few disc orbital times. In the RP
simulations, the distribution of clump masses and star-formation rates (SFRs)
normalized to their host disc is very similar at all redshifts. They exhibit a
truncated power-law with a slope slightly shallower than -2. Short-lived clumps
preferentially have young stellar ages, low masses, high gas fractions and
specific SFRs (sSFR), and they tend to populate the outer disc. The sSFR of
massive, long-lived clumps declines with age as they migrate towards the disc
centre, producing gradients in mass, stellar age, gas fraction, sSFR and
metallicity that distinguish them from short-lived clumps. Ex situ mergers make
up ~37% of the mass in clumps and ~29% of the SFR. They are more massive and
with older stellar ages than the in situ clumps, especially near the disc edge.
Roughly half the galaxies at redshifts z=4-1 are clumpy over a wide range of
stellar mass, with clumps accounting for ~3-30% of the SFR but ~0.1-3% of the
stellar mass.
|
The OTELO survey as a morphological probe. Last ten Gyr of galaxy
evolution. The mass--size relation up to z=2 | The morphology of galaxies provide us with a unique tool for relating and
understanding other physical properties and their changes over the course of
cosmic time. It is only recently that we have been afforded access to a wealth
of data for an unprecedented number galaxies thanks to large and deep surveys,
We present the morphological catalogue of the OTELO survey galaxies detected
with the Hubble Space Telescope (HST)-ACS F814W images. We explore various
methods applied in previous works to separate early-type (ET) and late-type
(LT) galaxies classified via spectral energy distribution (SED) fittings using
galaxy templates. Together with this article, we are releasing a catalogue
containing the main morphological parameters in the F606W and F814W bands
derived for more than 8\,000 sources. The morphological analysis is based on
the single-S\'ersic profile fit. We used the GALAPAGOS2 software to provide
multi-wavelength morphological parameters fitted simultaneously in two HST-ACS
bands. The GALAPAGOS2 software detects, prepares guess values for GALFTI-M, and
provides the best-fitting single-S\'ersic model in both bands for each source.
Stellar masses were estimated using synthetic rest-frame magnitudes recovered
from SED fittings of galaxy templates. The morphological catalogue is
complemented with concentration indexes from a separate SExtractor dual, high
dynamical range mode. A total of 8,812 sources were successfully fitted with
single-S\'ersic profiles. The analysis of a carefully selected sample of ~3,000
sources up to phot_z=2 is presented in this work, of which 873 sources were not
detected in previous studies. We found no statistical evidence for the
evolution of the low-mass end of mass-size relation for ET and LT since z=2.
Furthermore, we found a good agreement for the median size evolution for ET and
LT galaxies, for a given stellar mass, with the data from the literature.
|
Analysis of techni-dilaton as a dark matter candidate | The almost conformal dynamics of walking technicolor (TC) implies the
existence of the approximate scale invariance, which breaks down spontaneously
by the condensation of anti-techni and techni-fermions. According to the
Goldstone theorem, a spinless, parity-even particle, called techni-dilaton
(TD), then emerges at low energy. If TC exhibits an extreme walking, TD mass is
parametrically much smaller than that of techni-fermions (around 1 TeV), while
its decay constant is comparable to the cutoff scale of walking TC. We analyze
the light, decoupled TD as a dark matter candidate and study cosmological
productions of TD, both thermal and non-thermal, in the early Universe. The
thermal population is governed dominantly by single TD production processes
involving vertices breaking the scale symmetry, while the non-thermal
population is by the vacuum misalignment and is accumulated via harmonic and
coherent oscillations of misaligned classical TD fields. The non-thermal
population turns out to be dominant and large enough to explain the abundance
of presently observed dark matter, while the thermal population is highly
suppressed due to the large TD decay constant. Several cosmological and
astrophysical limits on the light, decoupled TD are examined to find that the
TD mass is constrained to be in a range between 0.01 eV and 500 eV. From the
combined constraints on cosmological productions and astrophysical
observations, we find that the light, decoupled TD can be a good dark matter
candidate with the mass around a few hundreds of eV for typical models of
(extreme) walking TC. We finally mention possible designated experiments to
detect the TD dark matter.
|
Noether symmetric minisuperspace model of $f(R)$ cosmology | We study the metric $f(R)$ cosmology using Noether symmetry approach by
utilizing the behavior of the corresponding Lagrangian under infinitesimal
generators of the desired symmetry. The existence of Noether symmetry of the
cosmological $f(R)$ minisuperspace helps us to find out the form of $f(R)$
function for which such symmetry exist. It is shown that the resulting form for
$f(R)$ yields a power law expansion for the cosmic scale factor. We also show
that in the corresponding Noether symmetric quantum model, the solutions to the
Wheeler-DeWitt equation can be expressed as a superposition of states of the
form $e^{iS}$. It is shown that in terms of such wavefunctions the classical
trajectories can be recovered.
|
The Moderate Cooling Flow Model and Feedback in Galaxy Formation | For the recent four years we have been studying feedback heating in cooling
flow (CF) clusters by AGN activity that inflate bubbles by jets; this short
contribution to a meeting summarizes our main results. To achieve our results
we had to self-consistently inflate the bubbles with jets, rather than inject
them artificially. Our main results are as follows
(1) Feedback mechanisms that are based on Bondi accretion fail. Instead, the
accretion to the central super-massive black hole (SMBH) is in the form of cold
dense blobs that fall-in from an extended region. (2) Slow massive wide (SMW)
jets, or rapidly precessing jets, can inflate bubbles similar to those observed
in CF clusters. (3) Contrary to some claims in the literature, the inflated
bubbles are stable for a relatively long time, becoming unstable only at later
times. (4) A single bubble inflation episode excites multiple sound waves and
shocks. These can then heat the intracluster medium (ICM). (5) Mixing of the
bubble material to the ICM is efficient, and can serve as a main heating
channel. (6) The heating processes work in all directions, and can explain the
heating of the ICM in CF in clusters and in galaxies.
|
Galaxy Formation: Merger vs Gas Accretion | According to the hierarchical model, small galaxies form first and merge
together to form bigger objects. In parallel, galaxies assemble their mass
through accretion from cosmic filaments. Recently, the increased spatial
resolution of the cosmological simulations have emphasised that a large
fraction of cold gas can be accreted by galaxies. In order to compare the role
of both phenomena and the corresponding star formation history, one has to
detect the structures in the numerical simulations and to follow them in time,
by building a merger tree.
|
Likelihood, Fisher information, and systematics of cosmic microwave
background experiments | Every experiment is affected by systematic effects that hamper the data
analysis and have the potential to ultimately degrade its performance. In the
case of probes of the cosmic microwave background (CMB) radiation, a minimal
set of issues to consider includes asymmetric beam functions, correlated noise,
and incomplete sky coverage. Presuming a simplified scanning strategy that
allows for an exact analytical treatment of the problem, we study the impact of
systematic effects on the likelihood function of the CMB power spectrum. We use
the Fisher matrix, a measure of the information content of a data set, for a
quantitative comparison of different experimental configurations. In addition,
for various power spectrum coefficients, we explore the functional form of the
likelihood directly, and obtain the following results: The likelihood function
can deviate systematically from a Gaussian distribution up to the highest
multipole values considered in our analysis. Treated exactly, realistic levels
of asymmetric beam functions and correlated noise do not by themselves decrease
the information yield of CMB experiments nor do they induce noticeable coupling
between multipoles. Masking large fractions of the sky, on the other hand,
results in a considerably more complex correlation structure of the likelihood
function. Combining adjacent power spectrum coefficients into bins can
partially mitigate these problems.
|
Measuring the transition to homogeneity with photometric redshift
surveys | We study the possibility of detecting the transition to homogeneity using
photometric redshift catalogs. Our method is based on measuring the fractality
of the projected galaxy distribution, using angular distances, and relies only
on observable quantites. It thus provides a way to test the Cosmological
Principle in a model-independent unbiased way. We have tested our method on
different synthetic inhomogeneous catalogs, and shown that it is capable of
discriminating some fractal models with relatively large fractal dimensions, in
spite of the loss of information due to the radial projection. We have also
studied the influence of the redshift bin width, photometric redshift errors,
bias, non-linear clustering, and surveyed area, on the angular homogeneity
index H2 ({\theta}) in a {\Lambda}CDM cosmology. The level to which an upcoming
galaxy survey will be able to constrain the transition to homogeneity will
depend mainly on the total surveyed area and the compactness of the surveyed
region. In particular, a Dark Energy Survey (DES)-like survey should be able to
easily discriminate certain fractal models with fractal dimensions as large as
D2 = 2.95. We believe that this method will have relevant applications for
upcoming large photometric redshift surveys, such as DES or the Large Synoptic
Survey Telescope (LSST).
|
Unfolding the matter distribution using 3-D weak gravitational lensing | Combining redshift and galaxy shape information offers new exciting ways of
exploiting the gravitational lensing effect for studying the large scales of
the cosmos. One application is the three-dimensional reconstruction of the
matter density distribution which is explored in this paper. We give a
generalisation of an already known minimum-variance estimator of the 3-D matter
density distribution that facilitates the combination of thin redshift slices
of sources with samples of broad redshift distributions for an optimal
reconstruction. We show how, in principle, intrinsic alignments of source
ellipticities or shear/intrinsic alignment correlations can be accommodated,
albeit these effects are not the focus of this paper. We describe an efficient
and fast way to implement the estimator on a contemporary desktop computer.
Analytic estimates for the noise and biases in the reconstruction are given.
The bias -- a spread and shift of structures in radial direction -- can be
expressed in terms of a radial PSF, comprising the limitations of the
reconstruction due to source shot-noise and the unavoidably broad lensing
kernel. We conclude that a 3-D mass-density reconstruction on galaxy cluster
scales is feasible but, for foreseeable surveys, a map with a S/N>~3 threshold
is limited to structures with M200>~10^14 Msol/h, or 7x10^14 Msol/h, at low to
moderate redshifts (z=0.1 or 0.6). However, we find that a heavily smoothed
full-sky map of the very large-scale density field may also be possible as the
S/N of reconstructed modes increases towards larger scales. Future improvements
of the method can be obtained by including higher-order lensing information
(flexion) which could also be implemented into our algorithm. [ABRIDGED]
|
The first shear measurements from precision weak lensing | We present an end-to-end methodology to measure the effects of weak lensing
on individual galaxy-galaxy systems exploiting their kinematic information.
Using this methodology, we have measured a shear signal from the velocity
fields of 18 weakly-lensed galaxies. We selected a sample of systems based only
on the properties of the sources, requiring them to be bright (apparent
$i$-band magnitude $ < 17.4$) and in the nearby Universe ($z < 0.15$). We have
observed the velocity fields of the sources with WiFeS, an optical IFU on a
2.3m telescope, and fitted them using a simple circular motion model with an
external shear. We have measured an average shear of $\langle \gamma \rangle =
0.020 \pm 0.008$ compared to a predicted $\langle \gamma_{pred} \rangle =
0.005$ obtained using median stellar-to-halo relationships from the literature.
While still a statistical approach, our results suggest that this new weak
lensing methodology can overcome some of the limitations of traditional
stacking-based techniques. We describe in detail all the steps of the
methodology and make publicly available all the velocity maps for the
weakly-lensed sources used in this study.
|
Properties of the Molecular Gas in Starburst Galaxies and AGN | There is growing evidence that the properties of the molecular gas in the
nuclei of starburst galaxies and in AGN may be very different from those seen
in Galactic star forming regions and that a high kinetic temperature in the
molecular gas may lead to a non-standard initial mass function in the next
generation of stars. Unfortunately, among the fundamental parameters derived
from molecular line observations, the kinetic temperature of the molecular gas
in external galaxies is often not well determined due to a lack of suitable
tracer molecules. We discuss the diagnostic power of selected transition lines
of formaldehyde (H_2CO), which can be used as a molecular thermometer as well
as an excellent tracer of the molecular gas density. As a proof of concept, we
present the results of our multi-transition line study of the H_2CO emission
from the prototypical starburst galaxy M82. Using our large velocity gradient
model, we tightly constrain the physical properties of the dense gas in the
prominent molecular lobes, completely independent of the standard "cloud
thermometer" ammonia (NH_3) or other molecular tracers. Our results agree well
with the properties of the high-excitation molecular gas component found in the
most comprehensive CO studies. Our observations also indicate that there may be
an asymmetry between the two molecular lobes.
|
Photospheric Magnitude Diagrams for Type II Supernovae: A Promising Tool
to Compute Distances | We develop an empirical color-based standardization for Type II supernovae
(SNe II), equivalent to the classical surface brightness method given in
Wesselink (1969). We calibrate it with SNe II with host galaxy distance
measured with Cepheids, and well-constrained shock breakout epoch and
extinction due to the host galaxy. We estimate the reddening with an analysis
of the B-V versus V-I color-color curves, similar to that of Natali et al.
(1994). With four SNe II meeting the above requirements, we build a
photospheric magnitude versus color diagram (similar to an HR diagram) with a
dispersion of 0.29 mag. We also show that when using time since shock breakout
instead of color as independent variable, the same standardization gives a
dispersion of 0.09 mag. Moreover, we show that the above time-based
standardization corresponds to the generalization of the standardized candle
method of Hamuy & Pinto (2002) for various epochs throughout the photospheric
phase. To test the new tool, we construct Hubble diagrams to different
subsamples of 50 low-redshift (cz<10^4 km s^-1) SNe II. For 13 SNe within the
Hubble flow (cz_CMB>3000 km s^-1) and with well-constrained shock breakout
epoch we obtain values of 68-69 km s^-1 Mpc^-1 for the Hubble constant, and an
mean intrinsic scatter of 0.12 mag or 6% in relative distances.
|
Linking low- to high-mass YSOs with Herschel-HIFI observations of water | Water probes the dynamics in young stellar objects (YSOs) effectively,
especially shocks in molecular outflows. It is a key molecule for exploring
whether the physical properties of low-mass protostars can be extrapolated to
massive YSOs. As part of the WISH key programme, we investigate the dynamics
and the excitation conditions of shocks along the outflow cavity wall as
function of source luminosity. Velocity-resolved Herschel-HIFI spectra of the
H2O 988, 752, 1097 GHz and 12CO J=10-9, 16-15 lines were analysed for 52 YSOs
with bolometric luminosities (L_bol) ranging from <1 to >10^5 L_sun. The
profiles of the H2O lines are similar, indicating that they probe the same gas.
We see two main Gaussian emission components in all YSOs: a broad component
associated with non-dissociative shocks in the outflow cavity wall (cavity
shocks) and a narrow component associated with quiescent envelope material.
More than 60% of the total integrated intensity of the H2O lines (L_H2O) comes
from the cavity shock component. The H2O line widths are similar for all YSOs,
whereas those of 12CO 10-9 increase slightly with L_bol. The excitation
analysis of the cavity shock component, performed with the non-LTE radiative
transfer code RADEX, shows stronger 752 GHz emission for high-mass YSOs, likely
due to pumping by an infrared radiation field. As previously found for CO, a
strong correlation with slope unity is measured between log(L_H2O) and
log(L_bol), which can be extrapolated to extragalactic sources. We conclude
that the broad component of H2O and high-J CO lines originate in shocks in the
outflow cavity walls for all YSOs, whereas lower-J CO transitions mostly trace
entrained outflow gas. The higher UV field and turbulent motions in high-mass
objects compared to their low-mass counterparts may explain the slightly
different kinematical properties of 12CO 10-9 and H2O lines from low- to
high-mass YSOs.
|
The X-shooter Spectral Library (XSL): Data Release 3 | We present the third data release (DR3) of the X-shooter Spectral Library
(XSL). This moderate-to-high resolution, near-ultraviolet-to-near-infrared
($350-2480$ nm, R $\sim$ 10 000) spectral library is composed of 830 stellar
spectra of 683 stars. DR3 improves upon the previous data release by providing
the combined de-reddened spectra of the three X-shooter segments over the full
$350-2480$ nm wavelength range. It also includes additional 20 M-dwarf spectra
from the ESO archive. We provide detailed comparisons between this library and
Gaia EDR3, MILES, NGSL, CaT library, and (E-)IRTF. The normalised rms deviation
is better than $D=0.05$ or 5$\%$ for the majority of spectra in common between
MILES (144 spectra of 180), NGSL (112$/$116), and (E-)IRTF (55$/$77) libraries.
Comparing synthetic colours of those spectra reveals only negligible offsets
and small rms scatter, such as the median offset(rms) 0.001$\pm$0.040 mag in
the (box1-box2) colour of the UVB arm,-0.004$\pm$0.028 mag in (box3-box4) of
the VIS arm, and -0.001$\pm$0.045 mag in (box2-box3) colour between the UVB and
VIS arms, when comparing stars in common with MILES. We also find an excellent
agreement between the Gaia published (BP-RP) colours and those measured from
the XSL DR3 spectra, with a zero median offset and an rms scatter of 0.037 mag
for 449 non-variable stars. The unmatched characteristics of this library,
which combine a relatively high resolution, a large number of stars, and an
extended wavelength coverage, will help us to bridge the gap between the
optical and the near-IR studies of intermediate and old stellar populations,
and to probe low-mass stellar systems.
|
Thermal Jeans fragmentation within 1000 AU in OMC-1S | We present subarcsecond 1.3 mm continuum ALMA observations towards the Orion
Molecular Cloud 1 South (OMC-1S) region, down to a spatial resolution of 74 AU,
which reveal a total of 31 continuum sources. We also present subarcsecond 7 mm
continuum VLA observations of the same region, which allow to further study
fragmentation down to a spatial resolution of 40 AU. By applying a Mean Surface
Density of Companions method we find a characteristic spatial scale at ~560 AU,
and we use this spatial scale to define the boundary of 19 `cores' in OMC-1S as
groupings of millimeter sources. We find an additional characteristic spatial
scale at ~2900 AU, which is the typical scale of the filaments in OMC-1S,
suggesting a two-level fragmentation process. We measured the fragmentation
level within each core and find a higher fragmentation towards the southern
filament. In addition, the cores of the southern filament are also the densest
(within 1100 AU) cores in OMC-1S. This is fully consistent with previous
studies of fragmentation at spatial scales one order of magnitude larger, and
suggests that fragmentation down to 40 AU seems to be governed by thermal Jeans
processes in OMC-1S.
|
Estimating distances from parallaxes IV: Distances to 1.33 billion stars
in Gaia Data Release 2 | For the vast majority of stars in the second Gaia data release, reliable
distances cannot be obtained by inverting the parallax. A correct inference
procedure must instead be used to account for the nonlinearity of the
transformation and the asymmetry of the resulting probability distribution.
Here we infer distances to essentially all 1.33 billion stars with parallaxes
published in the second \gaia\ data release. This is done using a weak distance
prior that varies smoothly as a function of Galactic longitude and latitude
according to a Galaxy model. The irreducible uncertainty in the distance
estimate is characterized by the lower and upper bounds of an asymmetric
confidence interval. Although more precise distances can be estimated for a
subset of the stars using additional data (such as photometry), our goal is to
provide purely geometric distance estimates, independent of assumptions about
the physical properties of, or interstellar extinction towards, individual
stars. We analyse the characteristics of the catalogue and validate it using
clusters. The catalogue can be queried on the Gaia archive using ADQL at
http://gea.esac.esa.int/archive/ and downloaded from
http://www.mpia.de/~calj/gdr2_distances.html .
|
Chiral Primordial Gravitational Waves from a Lifshitz Point | We study primordial gravitational waves produced during inflation in quantum
gravity at a Lifshitz point proposed by Ho${\rm\check{r}}$ava. Assuming
power-counting renormalizability, foliation preserving diffeomorphism
invariance, and the condition of detailed balance, we show that primordial
gravitational waves are circularly polarized due to parity violation. The
chirality of primordial gravitational waves is a quite robust prediction of
quantum gravity at a Lifshitz point which can be tested through observations of
cosmic microwave background radiation and stochastic gravitational waves.
|
Far-Infrared Luminous Supernova Remnant Kes 17 | We present the results of infrared (IR; 2.5--160 um) observations of the
supernova remnant (SNR) Kes 17 based on the data obtained with the AKARI and
Spitzer satellites. We first detect bright continuum emission of its western
shell in the mid- and far-IR wavebands together with its near-IR molecular line
emission. We also detect hidden mid-IR emission of its southern shell after
subtraction of the background emission in this region. The far-IR luminosity of
the western shell is ~ 8100 L_sun, which makes Kes 17 one of the few SNRs of
significant far-IR emission. The fittings of the spectral energy distribution
indicate the existence of two dust components: ~ 79 K (hot) and ~ 27 K (cold)
corresponding to the dust mass of ~ 6.2x10^{-4} M_sun and ~ 6.7 M_sun,
respectively. We suggest that the hot component represents the dust emission of
the material swept up by the SNR to its western and southern boundaries,
compatible with the distribution of radio continuum emission overlapping the
mid-IR emission in the western and southern shells. The existence of hot (~
2,000 K), shocked dense molecular gas revealed by the near-IR molecular line
emission in the western shell, on the other hand, suggests that the cold dust
component represents the dust emission related to the interaction between the
SNR and nearby molecular gas. The excitation conditions of the molecular gas
appear to be consistent with those from shocked, clumpy admixture gas of
different temperatures. We discuss three possibilities for the origin of the
bright far-IR emission of the cold dust in the western shell: the emission of
dust in the inter-clump medium of shocked molecular clouds, the emission of
dust in evaporating flows of molecular clouds engulfed by hot gas, and the
emission of dust of nearby molecular clouds illuminated by radiative shocks.
|
Feedback effects of aspherical supernovae explosions on galaxies | We investigate how explosions of aspherical supernovae (A-SNe) can influence
star formation histories and chemical evolution of dwarf galaxies by using a
new chemodynamical model. We mainly present the numerical results of two
comparative models so that the A-SN feedback effects on galaxies can be more
clearly seen. SNe originating from stars with masses larger than 30M_sun are
A-SNe in the "ASN" model whereas all SNe are spherical ones (S-SNe) in the
"SSN" model. Each S-SN and A-SN are assumed to release feedback energy of
10^{51} erg and 10^{52} erg, respectively, and chemical yields and feedback
energy of A-SN ejecta depend on angles between the axis of symmetry and the
ejection directions. We find that star formation can become at least by a
factor of ~3 lower in the ASN model in comparison with the SSN one owing to the
more energetic feedback of A-SNe. As a result of this, chemical evolution can
proceed very slowly in the ASN model. A-SN feedback effects can play a
significant role in the formation of giant gaseous holes and energetic gaseous
outflow and unique chemical abundances (e.g., high [Mg/Ca]). Based on these
results, we provide a number of implications of the A-SN feedback effects on
galaxy formation and evolution.
|
Corona-Australis DANCe. I. Revisiting the census of stars with Gaia-DR2
data | Corona-Australis is one of the nearest regions to the Sun with recent and
ongoing star formation, but the current picture of its stellar (and substellar)
content is not complete yet. We take advantage of the second data release of
the Gaia space mission to revisit the stellar census and search for additional
members of the young stellar association in Corona-Australis. We applied a
probabilistic method to infer membership probabilities based on a
multidimensional astrometric and photometric data set over a field of 128
deg$^{2}$ around the dark clouds of the region. We identify 313
high-probability candidate members to the Corona-Australis association, 262 of
which had never been reported as members before. Our sample of members covers
the magnitude range between $G\gtrsim5$ mag and $G\lesssim20$ mag, and it
reveals the existence of two kinematically and spatially distinct subgroups.
There is a distributed `off-cloud' population of stars located in the north of
the dark clouds that is twice as numerous as the historically known `on-cloud'
population that is concentrated around the densest cores. By comparing the
location of the stars in the HR-diagram with evolutionary models, we show that
these two populations are younger than 10 Myr. Based on their infrared excess
emission, we identify 28 Class II and 215 Class III stars among the sources
with available infrared photometry, and we conclude that the frequency of Class
II stars (i.e. `disc-bearing' stars) in the on-cloud region is twice as large
as compared to the off-cloud population. The distance derived for the
Corona-Australis region based on this updated census is $d=149.4^{+0.4}_{-0.4}$
pc, which exceeds previous estimates by about 20 pc.In this paper we provide
the most complete census of stars in Corona-Australis available to date that
can be confirmed with Gaia data.
|
The Galactic O-Star Spectroscopic Survey (GOSSS) | We present a massive spectroscopic survey of Galactic O stars, GOSSS, based
on new, high signal-to-noise ratio, R~2500 blue-violet digital observations
from both hemispheres. The sample size and selection criteria; the relationship
between GOSSS, the Galactic O-Star Catalog (GOSC), and three sister surveys
(OWN, IACOB, and Lucky Imaging); the current status; and our plans for the
future are discussed. We also show some of our first results, which include the
new Ofc category, two new examples of Of?p stars, a new atlas for O stars, and
the introduction of the O9.7 type for luminosity classes III to V. Finally, our
scientific objectives are discussed.
|
First predictions of the angular power spectrum of the astrophysical
gravitational wave background | We present the first predictions for the angular power spectrum of the
astrophysical gravitational wave background constituted of the radiation
emitted by all resolved and unresolved astrophysical sources. Its shape and
amplitude depend on both the astrophysical properties on galactic scales and on
cosmological properties. We show that the angular power spectrum behaves as
$C_{\ell}\propto 1/{\ell}$ on large scales and that relative fluctuations of
the signal are of order 30% at 100 Hz. We also present the correlations of the
astrophysical gravitational wave background with weak-lensing and galaxy
distribution. These numerical results pave the way to the study of a new
observable at the crossroad between general relativity, astrophysics and
cosmology.
|
The UV Continuum of z > 1 Star-forming Galaxies in the Hubble
Ultraviolet UltraDeep Field | We estimate the UV continuum slope, beta, for 923 galaxies in the range 1 < z
< 8 in the Hubble Ultradeep Field (HUDF). These data include 460 galaxies at 1
< z < 2 down to an absolute magnitude M_{UV} = -14 (~0.006 L*_{z=1}; 0.02
L*_{z=0}), comparable to dwarf galaxies in the local universe. We combine deep
HST/UVIS photometry in F225W, F275W, F336W wavebands (UVUDF) with recent data
from HST/WFC3/IR (HUDF12). Galaxies in the range 1 < z < 2 are significantly
bluer than local dwarf galaxies. We find their mean (median) values <beta> =
-1.382 (-1.830) +/- 0.002 (random) +/- 0.1 (systematic). We find comparable
scatter in beta (standard deviation = 0.43) to local dwarf galaxies and 30%
larger scatter than z > 2 galaxies. We study the trends of beta with redshift
and absolute magnitude for binned sub-samples and find a modest color-magnitude
relation, dbeta/dM = -0.11 +/- 0.01 and no evolution in dbeta/dM with redshift.
A modest increase in dust reddening with redshift and luminosity, Delta E(B-V)
~ 0.1, and a comparable increase in the dispersion of dust reddening at z < 2,
appears likely to explain the observed trends. At z > 2, we find trends that
are consistent with previous works; combining our data with the literature in
the range 1 < z < 8, we find a color evolution with redshift, dbeta/dz = -0.09
+/-0.01 for low luminosity (0.05 L*_{z=3}), and dbeta/dz = -0.06 +/-0.01 for
medium luminosity (0.25 L*_{z=3}) galaxies.
|
A Gemini view of the galaxy cluster RXC J1504-0248: insights on the
nature of the central gaseous filaments | We revisit the galaxy cluster RXC J1504-0248, a remarkable example of a
structure with a strong cool core in a near redshift ($z = 0.216$). We
performed a combined analysis using photometric and spectroscopic data obtained
at Gemini South Telescope. We estimated the cluster mass through gravitational
lensing, obtaining $M_{200} = 5.3\pm0.4 \times 10^{14}$ $h_{70}^{-1}$ M$_\odot$
within $R_{200} = 1.56 \pm 0.04$ $h^{-1}_{70}$ Mpc, in agreement with a virial
mass estimate. This cluster presents a prominent filamentary structure
associated to its BCG, located mainly along its major axis and aligned with the
X-ray emission. A combined study of three emission line diagnostic diagrams has
shown that the filament emission falls in the so-called transition region of
these diagrams. Consequently, several ionizing sources should be playing an
meaningful role. We have argued that old stars, often invoked to explain LINER
emission, should not be the major source of ionization. We have noticed that
most of the filamentary emission has line ratios consistent with the shock
excitation limits obtained from shock models. We also found that line fluxes
are related to gas velocities (here estimated from line widths) by power-laws
with slopes in the range expected from shock models. These models also show,
however, that only ~10% of H$\alpha$ luminosity can be explained by shocks. We
conclude that shocks probably associated to the cooling of the intracluster gas
in a filamentary structure may indeed be contributing to the filament nebular
emission, but can not be the major source of ionizing photons.
|
The chemical structure of young high-mass star-forming clumps: (II)
parsec-scale CO depletion and deuterium fraction of $\rm HCO^+$ | The physical and chemical properties of cold and dense molecular clouds are
key to understanding how stars form. Using the IRAM 30 m and NRO 45 m
telescopes, we carried out a Multiwavelength line-Imaging survey of the 70
$\mu$m dark and bright clOuds (MIAO). At a linear resolution of 0.1--0.5 pc,
this work presents a detailed study of parsec-scale CO depletion and $\rm
HCO^+$ deuterium (D-) fractionation toward four sources (G11.38+0.81,
G15.22-0.43, G14.49-0.13, and G34.74-0.12) included in our full sample. In each
source with $\rm T<20$ K and $n_{\rm H}\rm\sim10^4$--$\rm 10^5 cm^{-3}$, we
compared pairs of neighboring 70 $\mu$m bright and dark clumps and found that
(1) the $\rm H_2$ column density and dust temperature of each source show
strong spatial anticorrelation; (2) the spatial distribution of CO isotopologue
lines and dense gas tracers, such as 1--0 lines of $\rm H^{13}CO^+$ and $\rm
DCO^+$, are anticorrelated; (3) the abundance ratio between $\rm C^{18}O$ and
$\rm DCO^+$ shows a strong correlation with the source temperature; (4) both
the $\rm C^{18}O$ depletion factor and D-fraction of $\rm HCO^+$ show a robust
decrease from younger clumps to more evolved clumps by a factor of more than 3;
and (5) preliminary chemical modeling indicates chemical ages of our sources
are ${\sim}8\times10^4$ yr, which is comparable to their free-fall timescales
and smaller than their contraction timescales, indicating that our sources are
likely dynamically and chemically young.
|
Example of exponentially enhanced magnetic reconnection driven by a
spatially-bounded and laminar ideal flow | In laboratory and natural plasmas of practical interest, the spatial scale
$\Delta_d$ at which magnetic field lines lose distinguishability differs
enormously from the scale $a$ of magnetic reconnection across the field lines.
In the solar corona, plasma resistivity gives $a/\Delta_d\sim10^{12}$, which is
the magnetic Reynold number $R_m$. The traditional resolution of the paradox of
disparate scales is for the current density $j$ associated with the
reconnecting field $B_{rec}$ to be concentrated by a factor of $R_m$ by the
ideal evolution, so $ j\sim B_{rec}/\mu_0\Delta_d$. A second resolution is for
the ideal evolution to increase the ratio of the maximum to minimum separation
between pairs of arbitrarily chosen magnetic field lines,
$\Delta_{max}/\Delta_{min}$, when calculated at various points in time.
Reconnection becomes inevitable where $\Delta_{max}/\Delta_{min}\sim R_m$. A
simple model of the solar corona will be used for a numerical illustration that
the natural rate of increase in time is linear for the current density but
exponential for $\Delta_{max}/\Delta_{min}$. Reconnection occurs on a time
scale and with a current density enhanced by only $\ln(a/\Delta_d)$ from the
ideal evolution time and from the current density $B_{rec}/\mu_0a$. In both
resolutions, once a sufficiently wide region, $\Delta_r$, has undergone
reconnection, the magnetic field loses static force balance and evolves on an
Alfv\'enic time scale. The Alfv\'enic evolution is intrinsically ideal but
expands the region in which $\Delta_{max}/\Delta_{min}$ is large.
|
An AzTEC 1.1 mm survey of the GOODS-N field -- II. Multi-wavelength
identifications and redshift distribution | We present results from a multi-wavelength study of 29 sources (false
detection probabilities <5%) from a survey of the Great Observatories Origins
Deep Survey-North field at 1.1mm using the AzTEC camera. Comparing with
existing 850um SCUBA studies in the field, we examine differences in the source
populations selected at the two wavelengths. The AzTEC observations uniformly
cover the entire survey field to a 1-sigma depth of ~1mJy. Searching deep
1.4GHz VLA, and Spitzer 3--24um catalogues, we identify robust counterparts for
21 1.1mm sources, and tentative associations for the remaining objects. The
redshift distribution of AzTEC sources is inferred from available spectroscopic
and photometric redshifts. We find a median redshift of z=2.7, somewhat higher
than z=2.0 for 850um-selected sources in the same field, and our lowest
redshift identification lies at a spectroscopic redshift z=1.1460. We measure
the 850um to 1.1mm colour of our sources and do not find evidence for `850um
dropouts', which can be explained by the low-SNR of the observations. We also
combine these observed colours with spectroscopic redshifts to derive the range
of dust temperatures T, and dust emissivity indices $\beta$ for the sample,
concluding that existing estimates T~30K and $\beta$~1.75 are consistent with
these new data.
|
Infall Signatures in a Prestellar Core embedded in the High-Mass 70
$\mu$m Dark IRDC G331.372-00.116 | Using Galactic Plane surveys, we have selected a massive (1200 M$_\odot$),
cold (14 K) 3.6-70 $\mu$m dark IRDC G331.372-00.116. This IRDC has the
potential to form high-mass stars and, given the absence of current star
formation signatures, it seems to represent the earliest stages of high-mass
star formation. We have mapped the whole IRDC with the Atacama Large
Millimeter/submillimeter Array (ALMA) at 1.1 and 1.3 mm in dust continuum and
line emission. The dust continuum reveals 22 cores distributed across the IRDC.
In this work, we analyze the physical properties of the most massive core,
ALMA1, which has no molecular outflows detected in the CO (2-1), SiO (5-4), and
H$_2$CO (3-2) lines. This core is relatively massive ($M$ = 17.6 M$_\odot$),
subvirialized (virial parameter $\alpha_{vir}=M_{vir}/M=0.14$), and is barely
affected by turbulence (transonic Mach number of 1.2). Using the HCO$^+$ (3-2)
line, we find the first detection of infall signatures in a relatively massive,
prestellar core (ALMA1) with the potential to form a high-mass star. We
estimate an infall speed of 1.54 km s$^{-1}$ and a high accretion rate of 1.96
$\times$ 10$^{-3}$ M$_\odot$ yr$^{-1}$. ALMA1 is rapidly collapsing, out of
virial equilibrium, more consistent with competitive accretion scenarios rather
than the turbulent core accretion model. On the other hand, ALMA1 has a mass
$\sim$6 times larger than the clumps Jeans mass, being in an intermediate mass
regime ($M_{J}=2.7<M\lesssim$ 30 M$_\odot$), contrary to what both the
competitive accretion and turbulent core accretion theories predict.
|
The DRAO Planck Deep Fields: the polarization properties of radio
galaxies at 1.4 GHz | We present results of deep polarization imaging at 1.4 GHz with the Dominion
Radio Astrophysical Observatory as part of the DRAO Planck Deep Fields project.
This deep extragalactic field covers 15.16 square degrees centered at RA = 16h
14m and DEC = 54d 56', has an angular resolution of 42" x 62" at the field
center, and reaches a sensitivity of 55 microJy/beam in Stokes I and 45
microJy/beam in Stokes Q and U. We detect 958 radio sources in Stokes I of
which 136 are detected in polarization. We present the Euclidean-normalized
polarized differential source counts down to 400 microJy. These counts indicate
that sources have a higher degree of fractional polarization at fainter Stokes
I flux density levels than for brighter sources, confirming an earlier result.
We find that the majority of our polarized sources are steep-spectrum objects
with a mean spectral index of -0.77, and there is no correlation between
fractional polarization and spectral index. We also matched deep field sources
to counterparts in the Faint Images of the Radio Sky at Twenty Centimeters
catalogue. Of the polarized sources, 77% show structure at the arc-second scale
whereas only 38% of the sources with no detectable polarization show such
structure. The median fractional polarization is for resolved sources is 6.8%,
while it is 4.4% for compact objects. The polarized radio sources in our deep
field are predominantly those sources which are resolved and show the highest
degrees of fractional polarization, indicating that the lobe dominated
structure may be the source of the highly polarized sources. These resolved
radio galaxies dominate the polarized source counts at P_0 = sqrt(Q^2 + U^2) <
3 mJy.
|
Exploring the Interstellar Media of Optically Compact Dwarf Galaxies | We present new Very Large Array HI spectral line, archival Sloan Digital Sky
Survey, and archival Spitzer Space Telescope imaging of eight star-forming blue
compact dwarf galaxies that were selected to be optically compact (optical
radii less than 1 kpc). These systems have faint blue absolute magnitudes (M_B
>= -17), ongoing star formation (based on emission-line selection by the H
alpha or [OIII] lines), and are nearby (mean velocity = 3315 km/s = 45 Mpc).
One galaxy in the sample, ADBS 113845+2008, is found to have an HI halo that
extends 58 r-band scale lengths from its stellar body. In contrast, the rest of
the sample galaxies have HI radii to optical-scale-length ratios ranging from
9.3 to 26. The size of the HI disk in the "giant disk" dwarf galaxy ADBS
113845+2008 appears to be unusual as compared to similarly compact stellar
populations.
|
First space and kinematical analysis of newly discovered southern UFMGs
clusters with Gaia | The work on the kinematical parameters and spatial shape structure have been
performed with Gaia DR2 astrometry data of the new recently southern discovered
open clusters; UFMG 1, UFMG 2, and UFMG 3 in the vicinity (1.3 degrees radius)
of the rarely studied NGC 5999. The apexes positions with AD-diagram method are
computed for about 107, 168, 98, and 154 members of these star clusters,
respectively, our calculated values of apex coordinates, seems like: (A, D) =
(102.40 +/- 1.02 & -4.60 +/- 0.47; NGC 5999), (96.69 +/- 1.10 & -0.58 +/-
0.045; UFMG 1), (97.47 +/- 1.09 & 1.56 +/- 0.051; UFMG 2), and (98.65 +/- 1.12
& -0.26 +/- 0.060; UFMG 3). On the other hand, Velocity Ellipsoid Parameters
VEPs for those are also computed; e.g. space velocities due to Galactic
coordinates, dispersion velocities (sigma_1, sigma_2, sigma_3) due to matrix
elements for all ij, projected distances (X_sun, Y_sun, Z_sun) on the plane
disc, and the Solar elements (S_sun, l_A, b_A). According to an approximation
of spatial and kinematical shape, UFMGs and NGC 5999 seem to have a spatial
difference in their space locations but they appear to have formed in the same
region of the Galactic disc. The total cumulative mass MC; including total
number of main-sequence NMS and non-main-sequence Nnon-MS of these clusters
also evaluated here with a second-order polynomial of mass-luminosity relation
in order to get clusters tidal radii (pc). Finally, we concluded that NGC 5999,
UFMG 1, and UFMG 2 are dynamically relaxed (i.e. tau >> 1), and the fourth one
in non-relaxed.
|
Constraining the Rate of Protostellar Accretion Outbursts in the Orion
Molecular Clouds | Outbursts due to dramatic increases in the mass accretion rate are the most
extreme type of variability in young stellar objects. We searched for outbursts
among 319 protostars in the Orion molecular clouds by comparing 3.6, 4.5, and
24 micron photometry from the Spitzer Space Telescope to 3.4, 4.6, and 22
micron photometry from the Wide-field Infrared Survey Explorer (WISE) obtained
~ 6.5 yr apart. Sources that brightened by more than two standard deviations
above the mean variability at all three wavelengths were marked as burst
candidates, and they were inspected visually to check for false positives due
primarily to the reduced angular resolution of WISE compared to Spitzer. We
recovered the known burst V2775 Ori (HOPS 223) as well as a previously unknown
burst, HOPS 383, which we announced in an earlier paper. No other outbursts
were found. With observations over 6.5 yr, we estimate an interval of about
1000 yr between bursts with a 90% confidence interval of 690 to 40,300 yr. The
most likely burst interval is shorter than those found in studies of optically
revealed young stellar objects, suggesting that outbursts are more frequent in
protostars than in pre-main-sequence stars that lack substantial envelopes.
|
Wide Bandwidth Considerations for ALMA Band 2 | One of the main considerations in the ALMA Development Roadmap for the future
of operations beyond 2030 is to at least double its on-sky instantaneous
bandwidth capabilities. Thanks to the technological innovations of the past two
decades, we can now produce wider bandwidth receivers than were foreseen at the
time of the original ALMA specifications. In several cases, the band edges set
by technology at that time are also no longer relevant. In this memo, we look
into the scientific advantages of beginning with Band 2 when implementing such
wideband technologies. The Band 2 receiver system will be the last of the
original ALMA bands, completing ALMA's coverage of the atmospheric windows from
35-950 GHz, and is not yet covered by any other ALMA receiver. New receiver
designs covering and significantly extending the original ALMA Band 2 frequency
range (67-90 GHz) can now implement these technologies. We explore the
scientific and operational advantages of a receiver covering the full 67-116
GHz atmospheric window. In addition to technological goals, the ALMA
Development Roadmap provides 3 new key science drivers for ALMA, to probe: 1)
the Origins of Galaxies, 2) the Origins of Chemical Complexity, and 3) the
Origins of Planets. In this memo, we describe how the wide RF Band 2 system can
help achieve these goals, enabling several high-profile science programmes to
be executed uniquely or more effectively than with separate systems, requiring
an overall much lower array time and achieving more consistent calibration
accuracy: contiguous broad-band spectral surveys, measurements of deuterated
line ratios, and more generally fractionation studies, improved continuum
measurements (also necessary for reliable line flux measurements), simultaneous
broad-band observations of transient phenomena, and improved bandwidth for 3 mm
very long baseline interferometry (VLBI).
|
Optical observations of the nearby galaxy IC342 with narrow band [SII]
and H$\alpha$ filters. I | We present observations of the portion of the nearby spiral galaxy IC342
using narrow band [SII] and H$\alpha$ filters. These observations were carried
out in November 2011 with the 2m RCC telescope at Rozhen National Astronomical
Observatory in Bulgaria. In this paper we report coordinates, diameters,
H$\alpha$ and [SII] fluxes for 203 HII regions detected in two fields of view
in IC342 galaxy. The number of detected HII regions is 5 times higher than
previously known in these two parts of the galaxy.
|
Open issues in neutrino astrophysics | Neutrinos of astrophysical origin are messengers produced in stars, in
explosive phenomena like core-collapse supernovae, in the accretion disks
around black holes, or in the Earth's atmosphere. Their fluxes and spectra
encode information on the environments that produce them. Such fluxes are
modified in characteristic ways when neutrinos traverse a medium. Here our
current understanding of neutrino flavour conversion in media is summarized.
The importance of this domain for astrophysical observations is emphasized.
Examples are given of the fundamental properties that astrophysical neutrinos
have uncovered, or might reveal in the future.
|
Anisotropic Scalar Field Dark Energy with a Disformally Coupled
Yang-Mills Field | In the context of scalar-tensor theories, the inclusion of new degrees of
freedom coupled non-minimally to the gravitational sector might produce some
appealing effects on the cosmic expansion history. We investigate this premise
by including a canonical SU(2) Yang- Mills field to the total energy budget of
the universe coupled to the standard quintessential field by a disformal
transformation. From the dynamical system analysis, we study three cases of
cosmological interest that span most of the physical phase space of the model:
the uncoupled limit, the isotropic, and the Abelian cases. New scaling
solutions with a non-vanishing gauge field are found in all cases which can be
interesting for early cosmological scenarios. Some of these scaling solutions
even exhibit anisotropic features. Also, the background evolution of the
universe is studied by means of numerical analysis. As an interesting result,
the disformal coupling changes the equation of state of the gauge field from
radiation to matter at some stages of the evolution of the universe, thereby
the gauge field can contribute to some fraction of the total dark matter. We
have also quantified the redshift-dependent contribution of the gauge field in
the form of dark radiation during the radiation era to the effective number of
relativistic species. This depends essentially on the initial conditions and,
more importantly, on the disformal coupling function.
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Correlated Component Analysis for diffuse component separation with
error estimation on simulated Planck polarization data | We present a data analysis pipeline for CMB polarization experiments, running
from multi-frequency maps to the power spectra. We focus mainly on component
separation and, for the first time, we work out the covariance matrix
accounting for errors associated to the separation itself. This allows us to
propagate such errors and evaluate their contributions to the uncertainties on
the final products.The pipeline is optimized for intermediate and small scales,
but could be easily extended to lower multipoles. We exploit realistic
simulations of the sky, tailored for the Planck mission. The component
separation is achieved by exploiting the Correlated Component Analysis in the
harmonic domain, that we demonstrate to be superior to the real-space
application (Bonaldi et al. 2006). We present two techniques to estimate the
uncertainties on the spectral parameters of the separated components. The
component separation errors are then propagated by means of Monte Carlo
simulations to obtain the corresponding contributions to uncertainties on the
component maps and on the CMB power spectra. For the Planck polarization case
they are found to be subdominant compared to noise.
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Fast Diffusion of Magnetic Field in Turbulence and Origin of Cosmic
Magnetism | Turbulence is believed to play important roles in the origin of cosmic
magnetism. While it is well known that turbulence can efficiently amplify a
uniform or spatially homogeneous seed magnetic field, it is not clear whether
or not we can draw a similar conclusion for a localized seed magnetic field.
The main uncertainty is the rate of magnetic field diffusion on scales larger
than the outer scale of turbulence. To measure the diffusion rate of magnetic
field on those large scales, we perform a numerical simulation in which the
outer scale of turbulence is much smaller than the size of the system. We
numerically compare diffusion of a localized seed magnetic field and a
localized passive scalar. We find that diffusion of the magnetic field can be
much faster than that of the passive scalar and that turbulence can efficiently
amplify the localized seed magnetic field. Based on the simulation result, we
construct a model for fast diffusion of magnetic field. Our model suggests that
a localized seed magnetic field can fill the whole system in (L_sys/L) times
the large-eddy turnover time and that growth of the magnetic field stops in
max(15, L_sys/L) times the large-eddy turnover time, where L_sys is the size of
the system and $L$ is the driving scale. Our finding implies that, regardless
of the shape of the seed field, fast magnetization is possible in turbulent
systems, such as large-scale structure of the universe or galaxies.
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Kolmogorov analysis detecting radio and Fermi gamma-ray sources in
cosmic microwave background maps | The Kolmogorov stochasticity parameter is shown to act as a tool to detect
point sources in the cosmic microwave background (CMB) radiation temperature
maps. Kolmogorov CMB map constructed for the WMAP's 7-year datasets reveals
tiny structures which in part coincide with point radio and Fermi/LAT gamma-ray
sources. In the first application of this method, we identified several sources
not present in the then available 0FGL Fermi catalog. Subsequently they were
confirmed in the more recent and more complete 1FGL catalog, thus strengthening
the evidence for the power of this methodology.
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