16158256
X-RAY LUMINOSITY FUNCTIONS OF NORMAL GALAXIES IN THE GOODS
We present soft (0.5-2 keV) X-ray luminosity functions (XLFs) in the Great Observatories Origins Deep Survey (GOODS) fields, derived for galaxies at z ∼ 0.25 and 0.75. SED fitting was used to estimate photometric redshifts and separate galaxy types, resulting in a sample of 40 early-type galaxies and 46 late-type galaxies. We estimate k-corrections for both the X-ray/optical and Xray/NIR flux ratios, which facilitates the separation of AGN from the normal/starburst galaxies. We fit the XLFs with a power-law model using both traditional and Markov-Chain Monte Carlo (MCMC) procedures. A key advantage of the MCMC approach is that it explicitly takes into account upperlimits and allows errors on “derived” quantities such as luminosity densities to be computed directly (i.e., without potentially questionable assumptions concerning the propagation of errors). The slopes of the early-type galaxy XLFs tend to be slightly flatter than the late-type galaxy XLFs although the effect is significant at only the 90% and 97% levels for z∼ 0.25 and 0.75. The XLFs differ between z 0.5, at > 99% significance levels for early-type, late-type and all (early and latetype) galaxies. We also fit Schechter and log-normal models to the XLFs, fitting the low and high redshift XLFs for a given sample simultaneously assuming only pure luminosity evolution. In the case of log-normal fits, the results of MCMC fitting of the local FIR luminosity function were used as priors for the faint and bright-end slopes (similar to “fixing” these parameters at the FIR values
53462727
ALMA reveals a warm and compact starburst around a heavily obscured supermassive black hole at z = 4.75
We report ALMA Cycle 0 observations at 1.3 mm of LESS J033229.4-275619 (XID403), an ultraluminous infrared galaxy at z = 4.75 in the Chandra Deep Field South hosting a Compton-thick QSO. The source is not resolved in our data at a resolution of ~0.75 arcsec, placing an upper-limit of 2.5 kpc to the half-light radius of the continuum emission from heated-dust. After deconvolving for the beam size, however, we found a ~3σ indication of an intrinsic source size of 0.27 ± 0.08 arcsec (Gaussian FWHM), which would correspond to rhalf ~ 0.9 ± 0.3 kpc. We build the far-infrared SED of XID403 by combining datapoints from both ALMA and Herschel and fit it with a modified blackbody spectrum. For the first time, we measure the dust temperature Td = 58.5 ± 5.3 K in this system, which is comparable to what has been observed in other high-z submillimeter galaxies. The measured star formation rate is SFR = 1020 ± 150 M⊙ yr-1, in agreement with previous estimates at lower S/N. Based on the measured SFR and source size, we constrain the SFR surface density to be ΣSFR > 26M⊙ yr-1 kpc-2 (~200M⊙ yr-1 kpc-2 for rhalf ~ 0.9 kpc). The compactness of this starburst is comparable to what has been observed in other local and high-z starburst galaxies. If the gas mass measured from previous [CII] and CO(2–1) observations at low resolution is confined within the same dust region, assuming rhalf ~ 0.9 ± 0.3 kpc, this would produce a column density of NH ~ 0.3−1.1 × 1024 cm-2 towards the central SMBH, similar to the column density of ≈1.4 × 1024 cm-2 measured from the X-rays. Then, in principle, if both gas and dust were confined on sub-kpc scales, this would be sufficient to produce the observed X-ray column density without any need of a pc-scale absorber (e.g. the torus postulated by Unified Models). We speculate that the high compactness of star formation, together with the presence of a powerful AGN, likely produce an outflowing wind. This would be consistent with the ~350 km s-1 velocity shift observed between the Lyα emission and the submm lines ([CII], CO(2–1), [NII]) and with the highly-ionized Fe emission line at ~6.9 keV rest-frame tentatively observed in the X-ray spectrum. Finally, our observations show that, besides the mass, star formation rate and gas depletion timescale, XID403 has also the right size to be one of the progenitors of the compact quiescent massive galaxies seen at z ~ 3.
118412776
THE RECENT STAR FORMATION HISTORY OF NGC 5102
We present Hubble Space Telescope photometry of young stars in NGC 5102, a nearby gas-rich post-starburst S0 galaxy with a bright young stellar nucleus. We use the IAC-pop/MinnIAC algorithm to derive the recent star formation history in three fields in the bulge and disk of NGC 5102. In the disk fields, the recent star formation rate has declined monotonically and is now barely detectable, but a starburst is still in progress in the bulge and has added about 2% to the mass of the bulge over the last 200 Myr. Other studies of star formation in NGC 5102 indicate that about 20% of its stellar mass was added over the past Gyr. If this is correct, then much of the stellar mass of the bulge may have formed over this period. It seems likely that this star formation was fueled by the accretion of a gas-rich system with H I mass of about 2 × 109 M ☉, which has now been almost completely converted into stars. The large mass of recently formed stars and the blue colors of the bulge suggest that the current starburst, which is now fading, may have made a significant contribution to building the bulge of NGC 5102.
121992423
Bar Dissolution and Bulge Formation: an Example of Secular Dynamical Evolution in Galaxies
15537978
The Evolution of X-Ray Clusters and the Entropy of the Intracluster Medium
The thermodynamics of the diffuse, X-ray-emitting gas in clusters of galaxies is determined by gravitational processes associated with infalling gas, shock heating and adiabatic compression, and nongravitational processes such as heating by supernovae, stellar winds, activity in central galactic nuclei, and radiative cooling. The effect of gravitational processes on the thermodynamics of the intracluster medium (ICM) can be expressed in terms of the ICM entropy. The entropy is a convenient variable as long as cooling is negligible, since it remains constant during the phase of adiabatic compression during accretion into the potential well, and it shows a single steplike increase during shock heating. Observations indicate that nongravitational processes also play a key role in determining the distribution of entropy in the ICM. In particular, an entropy excess with respect to that produced by purely gravitational processes has been recently detected in the centers of low-temperature systems. This type of entropy excess is believed to be responsible for many other properties of local X-ray clusters, including the L-T relation and the flat density cores in clusters and groups. In this paper we assume that the entropy excess is present in the intergalactic medium (IGM) baryons before the gas is accreted by the dark matter halos and reaches high densities. We use a generalized spherical model to compute the X-ray properties of groups and clusters for a range of initial entropy levels in the IGM and for a range of mass scales, cosmic epochs, and background cosmologies. In particular, we follow the formation of adiabatic cores during the first stages of the gravitational collapse and the subsequent evolution of the central entropy due to radiative energy loss. The model predicts the statistical properties of the cluster population at a given epoch and also allows study of the evolution of single X-ray halos as a function of their age. We find that the statistical properties of the X-ray clusters strongly depend on the value of the initial background entropy. Assuming a constant, uniform value for the background entropy, the present-day X-ray data are well fitted for the following range of values of the adiabatic constant: K* ≡ kBT/μmpρ2/3 = (0.4 ± 0.1) × 1034 ergs cm2 g-5/3 for clusters with average temperatures kT > 2 keV and K* = (0.2 ± 0.1) × 1034 ergs cm2 g-5/3 for groups and clusters with average temperatures kBT < 2 keV. These values correspond to different excess energy per particle of kBT ≥ 0.1(K*/0.4 × 1034) keV. The dependence of K* on the mass scale can be well reproduced by an epoch-dependent external entropy: the relation K* = 0.8(1 + z)-1 × 1034 ergs cm2 g-5/3 fits the data over the whole temperature range. The model can be extended to include internal heating, but in this case the energy budget required to fit the X-ray properties would be much higher. Observations of both local and distant clusters can be used to trace the distribution and the evolution of the entropy in the cosmic baryons and to constrain the typical epoch and the source of the heating processes. The X-ray satellites Chandra and XMM can add to our knowledge of the history of the cosmic baryons, already derived from the high-redshift, low-density gas observed in the QSO absorption-line clouds, by imaging the hot, higher density plasma observed in groups and clusters of galaxies.
119538524
Cold Gas at High Redshift
We discuss the current observational and theoretical issues concerning cold gas at high redshift and present simulations showing how a number of observational issues can be resolved with planned future instrumentation.
7178771
Gamma Rays from Ultra-High-Energy Cosmic Rays in Cygnus A
Ultra-high-energy cosmic rays (UHECRs) accelerated in the jets of active galactic nuclei can accumulate in high magnetic field, ~100 kpc-scale regions surrounding powerful radio galaxies. Photohadronic processes involving UHECRs and photons of the extragalactic background light make ultrarelativistic electrons and positrons that initiate electromagnetic cascades, leading to the production of a γ-ray synchrotron halo. We calculate the halo emission in the case of Cygnus A and show that it should be detectable with the Fermi Gamma-Ray Space Telescope and possibly detectable with ground-based γ-ray telescopes if radio galaxies are the sources of UHECRs.
18301162
Off-shell effects in dilepton production from hot interacting mesons
The production of dielectrons in reactions involving a{sub 1} mesons and pions is studied. We compare results obtained with different phenomenological Lagrangians that have been used in connection with hadronic matter and finite nuclei. We insist on the necessity for those interactions to satisfy known empirical properties of the strong interaction. Large off-shell effects in dielectron production are found and some consequences for the interpretation of heavy ion data are outlined. We also compare with results obtained using experimentally extracted spectral functions. {copyright} {ital 1998} {ital The American Physical Society}
119353603
Hadronic production of thermal photons
We study the thermal emission of photons from hot and dense strongly interacting hadronic matter at temperatures close to the expected phase transition to the quark-gluon plasma (QGP). Earlier calculations of photon radiation from ensembles of interacting mesons are reexamined with additional constraints, including new production channels as well as an assessment of hadronic form factor effects. Whereas strangeness-induced photon yields turn out to be moderate, the hitherto not considered $t$-channel exchange of $\ensuremath{\omega}$ mesons is found to contribute appreciably for photon energies above $\ensuremath{\sim}1.5\phantom{\rule{0.3em}{0ex}}\text{GeV}$. The role of baryonic effects is assessed using existing many-body calculations of lepton pair production. We argue that our combined results constitute a rather realistic emission rate, appropriate for applications in relativistic heavy-ion collisions. Supplemented with recent evaluations of QGP emission, and an estimate for primordial (hard) production, we compute photon spectra at Super Proton Synchrotron (SPS), Relativistic Heavy Ion Collider (RHIC), and Large Hadron Collider (LHC) energies.