5949463
THE SPATIALLY RESOLVED STAR FORMATION LAW FROM INTEGRAL FIELD SPECTROSCOPY: VIRUS-P OBSERVATIONS OF NGC 5194
We investigate the relation between the star formation rate (SFR) surface density (SIGMA{sub SFR}) and the mass surface density of gas (SIGMA{sub gas}) in NGC 5194 (a.k.a. M51a, Whirlpool Galaxy). Visible Integral field Replicable Unit Spectrograph Prototype (VIRUS-P) integral field spectroscopy of the central 4.1 x 4.1 kpc{sup 2} of the galaxy is used to measure Halpha, Hbeta, [O III]lambda5007, [N II]lambdalambda6548,6584, and [S II]lambdalambda6717,6731 emission line fluxes for 735 regions approx170 pc in diameter. We use the Balmer decrement to calculate nebular dust extinctions, and correct the observed fluxes in order to accurately measure SIGMA{sub SFR} in each region. Archival H I 21 cm and CO maps with spatial resolution similar to that of VIRUS-P are used to measure the atomic and molecular gas surface density for each region. We present a new method for fitting the star formation law (SFL), which includes the intrinsic scatter in the relation as a free parameter, allows the inclusion of non-detections in both SIGMA{sub gas} and SIGMA{sub SFR}, and is free of the systematics involved in performing linear regressions over incomplete data in logarithmic space. After rejecting regions whose nebular spectrum is affected by the central active galactic nucleus in NGC 5194,more » we use the [S II]/Halpha ratio to separate spectroscopically the contribution from the diffuse ionized gas (DIG) in the galaxy, which has a different temperature and ionization state from those of H II regions in the disk. The DIG only accounts for 11% of the total Halpha luminosity integrated over the whole central region, but on local scales it can account for up to a 100% of the Halpha emission, especially in the inter-arm regions. After removing the DIG contribution from the Halpha fluxes, we measure a slope N = 0.82 +- 0.05, and an intrinsic scatter epsilon = 0.43 +- 0.02 dex for the molecular gas SFL. We also measure a typical depletion timescale tau=SIGMA{sub H{sub i+H{sub 2}}}/SIGMA{sub SFR}approx2 Gyr, in good agreement with recent measurements by Bigiel et al. The atomic gas density shows no correlation with the SFR, and the total gas SFL in the sampled density range closely follows the molecular gas SFL. Integral field spectroscopy allows a much cleaner measurement of Halpha emission line fluxes than narrow-band imaging, since it is free of the systematics introduced by continuum subtraction, underlying photospheric absorption, and contamination by the [N II] doublet. We assess the validity of different corrections usually applied in narrow-band measurements to overcome these issues and find that while systematics are introduced by these corrections, they are only dominant in the low surface brightness regime. The disagreement with the previous measurement of a super-linear molecular SFL by Kennicutt et al. is most likely due to differences in the fitting method. Our results support the recent evidence for a low, and close to constant, star formation efficiency (SFE =tau{sup -1}) in the molecular component of the interstellar medium. The data show an excellent agreement with the recently proposed model of the SFL by Krumholz et al. The large intrinsic scatter observed may imply the existence of other parameters, beyond the availability of gas, which are important in setting the SFR.« less
29731360
Submillimeter Follow-up of WISE-selected Hyperluminous Galaxies
We have used the Caltech Submillimeter Observatory (CSO) to follow-up a sample of Wide-field Infrared Survey Explorer (WISE) selected, hyperluminous galaxies, the so-called W1W2-dropout galaxies. This is a rare (∼1000 all-sky) population of galaxies at high redshift (peaks at z = 2–3), which are faint or undetected by WISE at 3.4 and 4.6 μm, yet are clearly detected at 12 and 22 μm. The optical spectra of most of these galaxies show significant active galactic nucleus activity. We observed 14 high-redshift ( z> 1.7) W1W2-dropout galaxies with SHARC-II at 350–850 μm, with nine detections, and observed 18 with Bolocam at 1.1 mm, with five detections. Warm Spitzer follow-up of 25 targets at 3.6 and 4.5 μm, as well as optical spectra of 12 targets, are also presented in the paper. Combining WISE data with observations from warm Spitzer and CSO, we constructed their mid-IR to millimeter spectral energy distributions (SEDs). These SEDs have a consistent shape, showing significantly higher mid-IR to submillimeter ratios than other galaxy templates, suggesting a hotter dust temperature. We estimate their dust temperatures to be 60–120 K using a single-temperature model. Their infrared luminosities are well over 10 13 L� . These SEDs are not well fitted with existing galaxy templates, suggesting they are a new population with very high luminosity and hot dust. They are likely among the most luminous galaxies in the universe. We argue that they are extreme cases of luminous, hot dust-obscured galaxies (DOGs), possibly representing a short evolutionary phase during galaxy merging and evolution. A better understanding of their long-wavelength properties needs ALMA as well as Herschel data.
118401675
The Diskionary: A Glossary of Terms Commonly Used for Disks and Related Objects, First Edition
Based on a panel discussion at the meeting "New Light on Young Stars: Spitzer's View of Circumstellar Disks", we provide some definitions of common usage of terms describing disks and related objects.
119498034
Submillimeter Dust Continuum Studies of Low and High Mass Star Formation
Studying the physical environments of low mass and high mass cores using dust continuum emission provides important observational constraints on theoretical models of star formation. The motivation and procedure for modeling dust continuum emission is reviewed and the results of recent surveys towards low mass and high mass star forming regions are compared.
119231909
THE SPITZER c2d SURVEY OF NEARBY DENSE CORES. IX. DISCOVERY OF A VERY LOW LUMINOSITY OBJECT DRIVING A MOLECULAR OUTFLOW IN THE DENSE CORE L673-7
We present new infrared, submillimeter, and millimeter observations of the dense core L673-7 and report the discovery of a low-luminosity, embedded Class 0 protostar driving a molecular outflow. L673-7 is seen in absorption against the mid-infrared background in 5.8, 8, and 24 {mu}m Spitzer images, allowing for a derivation of the column density profile and total enclosed mass of L673-7, independent of dust temperature assumptions. Estimates of the core mass from these absorption profiles range from 0.2to4.5 M{sub sun}. Millimeter continuum emission indicates a mass of {approx}2 M{sub sun}, both from a direct calculation assuming isothermal dust and from dust radiative transfer models constrained by the millimeter observations. We use dust radiative transfer models to constrain the internal luminosity of L673-7, defined to be the luminosity of the central source and excluding the luminosity from external heating, to be L{sub int} = 0.01-0.045 L{sub sun}, with L{sub int} {approx} 0.04 L{sub sun} the most likely value. L673-7 is thus classified as a very low luminosity object (VeLLO), and is among the lowest luminosity VeLLOs yet studied. We calculate the kinematic and dynamic properties of the molecular outflow in the standard manner. From the outflow properties and standard assumptions regarding themore » driving of outflows, we calculate the time-averaged protostellar mass accretion rate, total protostellar mass accreted, and expected accretion luminosity to be {>=}1.2 x 10{sup -6} (sin i)/(co{sup 2} i) M{sub sun} yr{sup -1}, M{sub acc{>=}}0.07 1/cos i M{sub sun}, and L{sub acc} {>=} 0.36 L{sub sun}, respectively. The discrepancy between this calculated L{sub acc} and the L{sub int} derived from dust radiative transfer models indicates that the current accretion rate is much lower than the average rate over the lifetime of the outflow. Although the protostar embedded within L673-7 is consistent with currently being substellar, it is unlikely to remain as such given the substantial mass reservoir remaining in the core.« less
119073347
Fragmentation and Evolution of Molecular Clouds. I. Algorithm and First Results
We present a series of simulations of the fragmentation of a molecular cloud, leading to the formation of a cluster of protostellar cores. We use Gaussian initial conditions with a power spectrum P(k) ∝ k-2, assume an isothermal equation of state, and neglect turbulence and magnetic fields. The purpose of these simulations is to address a specific numerical problem called artificial fragmentation, which plagues simulations of cloud fragmentation. We argue that this is a serious problem, and that the only reasonable and practical way to address it within the smoothed particle hydrodynamics (SPH) algorithm is to use a technique called particle splitting. We performed three simulations, with Ngen = 0, 1, and 2 levels of particle splitting. All simulations start up with 643 SPH particles, but their effective resolutions correspond to 643, 1283, and 2563 particles, respectively. The third simulation properly resolves the Jeans mass throughout the entire system, at all times, thus preventing artificial fragmentation. The high resolution of our simulations results in the formation of a large number of protostellar cores, nearly 3000 for the largest simulation. The final mass distribution of cores is lognormal, and the distribution shifts down in mass as the resolution improves. The width of the distribution is about 1.5 (e.g., a factor of 30 in the mass), and the low-mass edge of the distribution corresponds to the lowest core mass that the code can resolve. This result differs from previous claims of a relationship between the mean of the distribution and the initial Jeans mass.
118966544
Chiral dynamics from AdS space
We study the low energy dynamics of pions in a gravity dual of chiral symmetry breaking. The string theory construction consists of a probe D7 brane in the Constable-Myers nonsupersymmetric background, which has been shown to describe chiral symmetry breaking in the pattern of QCD. We expand the D7 brane's Dirac-Born-Infeld action for fluctuations that correspond to the Goldstone mode and show that they take the form of a nonlinear chiral Lagrangian. We numerically compute the quark condensate, pion decay constant, and higher order Gasser-Leutwyler coefficients. We find their form is consistent with naive dimensional analysis estimates. We also explore the gauging of the quark's chiral symmetries and the vector meson spectrum.
119123061
Chiral phase transitions and quantum critical points of the D3/D7(D5) system with mutually perpendicular E and B fields at finite temperature and density
We study chiral symmetry restoration with increasing temperature and density in gauge theories subject to mutually perpendicular electric and magnetic fields using holography. We determine the chiral symmetry breaking phase structure of the D3/D7 and D3/D5 systems in the temperature-density-electric field directions. A magnetic field may break the chiral symmetry and an additional electric field induces Ohm and Hall currents as well as restoring the chiral symmetry. At zero temperature the D3/D5 system displays a line of holographic BKT phase transitions in the density-electric field plane, while the D3/D7 system shows a mean-field phase transition. At intermediate temperatures, the transitions in the density-electric field plane are of first order at low density, transforming to second order at critical points as density rises. At high temperature the transition is only ever first order.
16511153
A stable supergravity dual of non-supersymmetric glue
We study nonsupersymmetric fermion mass and condensate deformations of the AdS conformal field theory correspondence. The five dimensional supergravity flows are lifted to a complete and remarkably simple ten dimensional background. A brane probe analysis shows that when all the fermions have an equal mass a positive mass is generated for all six scalar fields leaving nonsupersymmetric Yang-Mills theory in the deep infrared. We numerically determine the potential, produced by the background, in the Schrodinger equation relevant to the study of O++ glueballs. The potential is a bounded well, providing evidence of stability and for a discrete, confined spectrum. The geometry can also describe the supergravity background around an (unstable) fuzzy 5-brane.
54800654
Holography of the conformal window
Inspired by the model of Jarvinen and Kiritsis, we present a simple holographic model for the onset of chiral symmetry breaking at the edge of the conformal window in QCD in the Veneziano limit. Our most naive model enforces the QCD two-loop running coupling on a D3/D7 holographic brane system. The mass of the holographic field, describing the chiral condensate in the model, is driven below the Breitenlohner-Freedman bound when the running is sufficiently strong, triggering chiral symmetry breaking for Nf/Nc<2.9. This model though contains too great a remnant of supersymmetry and does not correctly encode the perturbative anomalous dimensions of QCD. In a second model we impose the QCD anomalous dimension result and find chiral symmetry breaking sets in for Nf/Nc=4 at a Berezinsky-Kosterlitz-Thouless-type phase transition. In this case the transition is triggered when the anomalous dimension of the mass operator γm=1.
15006058
An Effective field theory approach to color superconductivity at high quark density
Abstract We investigate the Fermi Liquid theory of high density QCD. Using the renormalization group (RG), we determine the behavior of effective fermion interactions near the Fermi surface. At sufficiently high densities the matching between the Fermi Liquid theory and QCD can be accomplished in perturbation theory and a reliable calculation of Cooper pair formation performed, modulo the existence of screening masses for the gluon. The presence of a chemical potential leads to different RG flows for sub-components of the effective interactions which would ordinarily be linked by Lorentz invariance. We also study instanton-induced operators and find that near the Fermi surface they are likely to be subdominant relative to operators induced by perturbative gluon exchange. We discuss the implications of our results for the phase structure of QCD at finite baryon density and temperature.