We present $Chandra$ X-ray point source catalogs for 9 Hickson Compact Groups (HCGs, 37 galaxies) at distances $34 - 89$ Mpc. We perform detailed X-ray point source detection and photometry, and interpret the point source population by means of simul
ated hardness ratios. We thus estimate X-ray luminosities ($L_X$) for all sources, most of which are too weak for reliable spectral fitting. For all sources, we provide catalogs with counts, count rates, power-law indices ($Gamma$), hardness ratios, and $L_X$, in the full ($0.5-8.0$ keV), soft ($0.5-2.0$ keV) and hard ($2.0-8.0$ keV) bands. We use optical emission-line ratios from the literature to re-classify 24 galaxies as star-forming, accreting onto a supermassive black hole (AGNs), transition objects, or low-ionization nuclear emission regions (LINERs). Two-thirds of our galaxies have nuclear X-ray sources with $Swift$/UVOT counterparts. Two nuclei have $L_{X,{rm 0.5-8.0 keV}}$~$ > 10^{42}$ erg s$^{-1}$, are strong multi-wavelength AGNs and follow the known $alpha_{rm OX}- u L_{ u,rm near UV}$ correlation for strong AGNs. Otherwise, most nuclei are X-ray faint, consistent with either a low-luminosity AGN or a nuclear X-ray binary population, and fall in the non-AGN locus in $alpha_{rm OX}- u L_{ u,rm near UV}$ space, which also hosts other, normal, galaxies. Our results suggest that HCG X-ray nuclei in high specific star formation rate spiral galaxies are likely dominated by star formation, while those with low specific star formation rates in earlier types likely harbor a weak AGN. The AGN fraction in HCG galaxies with $M_R le -20$ and $L_{X,{rm 0.5-8.0 keV}} ge 10^{41}$ erg s$^{-1}$ is $0.08^{+0.35}_{-0.01}$, somewhat higher than the $sim 5%$ fraction in galaxy clusters.
We present the largest-scale comparison to date between observed extragalactic X-ray binary (XRB) populations and theoretical models of their production. We construct observational X-ray luminosity functions (oXLFs) using Chandra observations of 12 l
ate-type galaxies from the Spitzer Infrared Nearby Galaxy Survey (SINGS). For each galaxy, we obtain theoretical XLFs (tXLFs) by combining XRB synthetic models, constructed with the population synthesis code StarTrack, with observational star formation histories (SFHs). We identify highest-likelihood models both for individual galaxies and globally, averaged over the full galaxy sample. Individual tXLFs successfully reproduce about half of oXLFs, but for some galaxies we are unable to find underlying source populations, indicating that galaxy SFHs and metallicities are not well matched and/or XRB modeling requires calibration on larger observational samples. Given these limitations, we find that best models are consistent with a product of common envelope ejection efficiency and central donor concentration ~=0.1, and a 50% uniform -- 50% twins initial mass-ratio distribution. We present and discuss constituent subpopulations of tXLFs according to donor, accretor and stellar population characteristics. The galaxy-wide X-ray luminosity due to low-mass and high-mass XRBs, estimated via our best global model tXLF, follows the general trend expected from the L_x - star formation rate and L_x - stellar mass relations of Lehmer et al 2010. Our best models are also in agreement with modeling of the evolution both of XRBs over cosmic time and of the galaxy X-ray luminosity with redshift.
We present Swift UVOT (1600-3000A) 3-band photometry for 41 galaxies in 11 nearby (<4500km/s) Hickson Compact Groups (HCGs) of galaxies. We use the uvw2-band (2000A) to estimate the dust-unobscured component, SFR_UV, of the total star-formation rate,
SFR_T. We use Spitzer MIPS 24-micron photometry to estimate SFR_IR, the dust-obscured component of SFR_T. We obtain SFR_T=SFR_UV+SFR_IR. Using 2MASS K_s band based stellar mass, M*, estimates, we calculate specific SFRs, SSFR=SFR_T/M*. SSFR values show a clear and significant bimodality, with a gap between low (<~3.2x10^-11 / yr) and high SSFR (>~1.2x10^-10 / yr) systems. All galaxies with MIR activity index a_IRAC <= 0 (>0) are in the high- (low-) SSFR locus, as expected if high levels of star-formation power MIR emission from polycyclic aromatic hydrocarbon molecules and a hot dust continuum. All elliptical/S0 galaxies are in the low-SSFR locus, while 22 out of 24 spirals/irregulars are in the high-SSFR locus, with two borderline cases. We divide our sample into three subsamples (I, II and III) according to decreasing HI-richness of the parent galaxy group to which a galaxy belongs. Consistent with the SSFR and a_IRAC bimodality, 12 out of 15 type-I (11 out of 12 type-III) galaxies are in the high- (low-) SSFR locus, while type II galaxies span almost the full range of SSFR values. Unlike HCG galaxies, galaxies in a comparison quiescent SINGS sub-sample are continuously distributed both in SSFR and a_IRAC. Any uncertainties can only further enhance the SSFR bimodality. These results suggest that an environment characterized by high galaxy number-densities and low galaxy velocity-dispersions, such as the one found in compact groups, plays a key role in accelerating galaxy evolution by enhancing star-formation processes in galaxies and favoring a fast transition to quiescence.(abridged)
Context: We use the first XMM serendipitous source catalogue (1XMM) to compile a sample of normal X-ray galaxies Aims: We seek to expand the database of X-ray selected normal galaxies at intermediate redshifts and examine the relation between X-ray
emission and star formation for late-type systems Methods: The candidates are selected based on their X-ray (soft spectra), X-ray to optical [log(fx/fo)<-2] and optical (extended sources) properties. 44 candidates are found and 35 are spectroscopically observed with the Australian National Universitys 2.3m telescope to examine their nature. Results: Of the 35 sources observed, 2 are AGN, 11 emission line galaxies, 12 absorption line galaxies, 6 have featureless spectra while 4 are associated with Galactic stars. We combine our emission line sample with earlier works forming the most comprehensive X-ray selected galaxy sample for the study of the X-ray luminosity to the Halpha luminosity - a well-calibrated star-formation indicator - relation. Conclusions: We find that the X-ray luminosity strongly correlates with the Halpha luminosity, suggesting that the X-rays efficiently trace the star-formation.
We compile one of the largest ever samples to probe the X-ray normal galaxy luminosity function and its evolution with cosmic time. In particular, we select 207 galaxies (106 late and 101 early-type systems) from the Chandra Deep Field North and Sout
h surveys, the Extended Chandra Deep Field South and the XBOOTES survey. We derive the luminosity function separately for the total (early+late), the early and the late-type samples using both a parametric maximum likelihood method, and a variant of the non-parametric 1/V_m method. Although the statistics is limited, we find that the total (early+late) galaxy sample is consistent with a Pure Luminosity evolution model where the luminosity evolves according to L(z) ~ (1+z)^2.2. The late-type systems appear to drive this trend while the early-type systems show much weaker evidence for evolution. We argue that the X-ray evolution of late-type systems is consistent with that of blue galaxies in the optical. In contrast there is a mismatch between the X-ray evolution of early-type systems and that of red galaxies at optical wavelengths.
AIMS: We have compiled one of the largest normal-galaxy samples ever to probe X-ray luminosity function evolution separately for early and late-type systems. METHODS: We selected 207 normal galaxies up to redshift z~1.4, with data from four major C
handra X-ray surveys, namely the Chandra deep fields (north, south and extended) and XBootes, and a combination of X-ray and optical criteria. We used template spectral energy-distribution fitting to obtain separate early- and late-type sub-samples, made up of 101 and 106 systems, respectively. For the full sample, as well as the two sub-samples, we obtained luminosity functions using both a non-parametric and a parametric, maximum-likelihood method. RESULTS: For the full sample, the non-parametric method strongly suggests luminosity evolution with redshift. The maximum-likelihood estimate shows that this evolution follows ~(1+z)^k_total, k_total=2.2+-0.3. For the late-type sub-sample, we obtained k_late=2.4^+1.0_-2.0. We detected no significant evolution in the early-type sub-sample. The distributions of early and late-type systems with redshift show that late types dominate at z>~0.5 and hence drive the observed evolution for the total sample. CONCLUSIONS: Our results support previous results in X-ray and other wavebands, which suggests luminosity evolution with k=2-3.
