B. D. Lehmer

A Chandra Perspective on Galaxy-wide X-ray Binary Emission and its Correlation with Star Formation Rate and Stellar Mass: New Results from Luminous Infrared Galaxies

We present newChandra observations that complete a sample of seventeen (17) luminous infrared galaxies (LIRGs) with D< 60 Mpc and low Galactic column densities of NH 5 × 10 20 cm −2 . The LIRGs in our sample have total infrared (8–1000 μm) luminosities in the range of LIR ≈ (1–8) × 10 11 L� . The high-resolution imaging and X-ray spectral information from our Chandra observations allow us to measure separately X-ray contributions from active galactic nuclei and normal galaxy processes (e.g., X-ray binaries and hot gas). We utilized total infrared plus UV luminosities to estimate star formation rates (SFRs) and K-band luminosities and optical colors to estimate stellar masses (M� ) for the sample. Under the assumption that the galaxy-wide 2–10 keV luminosity (L gal ) traces the combined emission from high-mass X-ray binaries (HMXBs) and low-mass X-ray binaries, and that the power output from these components is linearly correlated with SFR and M� , respectively, we constrain the relation L gal = αM� + βSFR. To achieve this, we construct a Chandra-based data set composed of our new LIRG sample combined with additional samples of less actively star-forming normal galaxies and more powerful LIRGs and ultraluminous infrared galaxies (ULIRGs) from the literature. Using these data, we measure best-fit values of α = (9.05 ± 0.37) × 10 28 erg s −1 M −1 ...

COLOR-MAGNITUDE RELATIONS OF ACTIVE AND NON-ACTIVE GALAXIES IN THE CHANDRA DEEP FIELDS: HIGH-REDSHIFT CONSTRAINTS AND STELLAR-MASS SELECTION EFFECTS

We extend color-magnitude relations for moderate-luminosity X-ray active galactic nucleus (AGN) hosts and non-AGN galaxies through the galaxy formation epoch (z ≈ 1-4) in the Chandra Deep Field-North and Chandra Deep Field-South (CDF-N and CDF-S, respectively; jointly CDFs) surveys. This study was enabled by the deepest available X-ray data from the 2 Ms CDF surveys as well as complementary ultradeep multiwavelength data in these regions. We utilized analyses of color-magnitude diagrams (CMDs) to assess the role of moderate-luminosity AGNs in galaxy evolution. First, we confirm some previous results and extend them to higher redshifts, finding, for example, that (1) there is no apparent color bimodality (i.e., the lack of an obvious red sequence and blue cloud) for AGN hosts from z ≈ 0to2, but non-AGN galaxy color bimodality exists up to z ≈ 3 and the relative fraction of red-sequence galaxies generally increases as the redshift decreases (consistent with a blue-to-red migration of galaxies), (2) most AGNs reside in massive hosts and the AGN fraction rises strongly toward higher stellar mass, up to z ≈ 2-3, and (3) the colors of both AGN hosts and non-AGN galaxies become redder as the stellar mass increases, up to z ≈ 2-3. Second, we point out that, in order to obtain a complete and reliable picture, it is critical to use mass-matched samples to examine color-magnitude relations of AGN hosts and non-AGN galaxies. We show that for mass-matched samples up to z ≈ 2-3, AGN hosts lie in the same region of the CMD as non-AGN galaxies; i.e., there is no specific clustering of AGN hosts in the CMD around the red sequence, the top of the blue cloud, or the green valley in between. The AGN fraction (≈ 10%) is mostly independent of host-galaxy color, providing an indication of the duty cycle of supermassive black hole growth in typical massive galaxies. These results are in contrast to those obtained with non-mass-matched samples where there is apparent AGN clustering in the CMD and the AGN fraction generally increases as the color becomes redder. We also find, for mass-matched samples, that the star formation rates of AGN hosts are typically a factor of ≈ 2-3 larger than those of non-AGN galaxies at z ≈ 0-1, whereas this difference diminishes at z ≈ 1-3. With mass-selection effects taken into account, we find that almost all of the results obtained in this work can reasonably be explained by two main ingredients, color-mass correlation (i.e., X-ray AGNs preferentially reside in massive galaxies that generally tend to be redder than less-massive galaxies) and passive or secular evolution of galaxies. Our results show that the presence of moderate-luminosity AGN activity does not have a significant effect on the colors of galaxies and thus tightly constrain any effects from moderate-luminosity AGN feedback upon color-magnitude properties over the ≈ 80% of cosmic time during which most of galaxy formation occurred.

THE 4 Ms CHANDRA DEEP FIELD-SOUTH NUMBER COUNTS APPORTIONED BY SOURCE CLASS: PERVASIVE ACTIVE GALACTIC NUCLEI AND THE ASCENT OF NORMAL GALAXIES

This article presents cumulative and differential number-count measurements for the recently completed 4 Ms Chandra Deep Field-South survey.

A submillimetre galaxy at z=4.76 in the LABOCA survey of the Extended Chandra Deep Field South

We report on the identification of the highest redshift submillimetre-selected source currently known LESS J033229.4−275619. This source was detected in the Large Apex Bolometer Camera (LABOCA) Extended Chandra Deep Field-South (ECDF-S) Submillimetre Survey (LESS), a sensitive 870-μm survey (σ_(870 μm)∼ 1.2 mJy) of the full 30 × 30 arcmin_2 ECDF-S with the LABOCA on the Atacama Pathfinder Experiment telescope. The submillimetre emission is identified with a radio counterpart for which optical spectroscopy provides a redshift of z= 4.76 . We show that the bolometric emission is dominated by a starburst with a star formation rate of ∼1000 M_⊙ yr^(−1), although we also identify a moderate luminosity active galactic nucleus (AGN) in this galaxy. Thus it has characteristics similar to those of z∼ 2 submillimetre galaxies (SMGs), with a mix of starburst and obscured AGN signatures. This demonstrates that ultraluminous starburst activity is not just restricted to the hosts of the most luminous (and hence rare) quasi-stellar objects at z∼ 5 , but was also occurring in less extreme galaxies at a time when the Universe was less than 10 per cent of its current age. Assuming that we are seeing the major phase of star formation in this galaxy, then we demonstrate that it would be identified as a luminous distant red galaxy at z∼ 3 and that the current estimate of the space density of z > 4 SMGs is only sufficient to produce ≳10 per cent of the luminous red galaxy population at these early times. However, this leaves open the possibility that some of these galaxies formed through less intense, but more extended star formation events. If the progenitors of all of the luminous red galaxies at z∼ 3 go through an ultraluminous starburst at z≳ 4 then the required volume density of z > 4 SMGs will exceed that predicted by current galaxy formation models by more than an order of magnitude.

Identifications and Photometric Redshifts of the 2 Ms Chandra Deep Field-South Sources

We present reliable multiwavelength identifications and hi gh-quality photometric redshifts for the 462 X-ray sources in the � 2 Ms Chandra Deep Field-South survey. Source identifications are carrie d out using deep optical‐to‐radio multiwavelength catalogs, and are then combined to create lists of primary and secondary counterparts for the X-ray sources. We identified reliable c ounterparts for 442 (95.7%) of the X-ray sources, with an expected false-match probability of � 6.2%; we also selected four additional likely counterparts. The majority of the other 16 X-ray sources appear to be off-nuclear sources, sources associated with galaxy groups and clusters, high-redshift active galactic nuclei (AGNs) , or spurious X-ray sources. A likelihood-ratio method is used for source matching, which effectively reduces the false-match probability at faint magnitudes compared to a simple error-circle matching method. We construct a master photometric catalog for the identified X-ray sources including up to 42 bands of UV‐to‐infrared data, and then calculate their photometric redshifts (photo-z’s). High accuracy in the derived photo-z’s is acco mplished owing to (1) the up-to-date photometric data covering the full spectral energy distributions (SEDs ) of the X-ray sources, (2) more accurate photometric data as a result of source deblending for � 10% of the sources in the infrared bands and a few percent in the optical and near-infrared bands, (3) a set of 265 galaxy, AGN, and galaxy/AGN hybrid templates carefully constructed to best represent all possible SEDs, (4) the Zurich Extragalactic Bayesian Redshift Analyzer (ZEBRA) used to derive the photo-z’s, which corrects the SED templat es to best represent the SEDs of real sources at different redshifts and thus improves the photo-z quality. The reliability of the photo-z’s is evaluated using the subsample of 220 sources with secure spectroscopic redshifts. We achieve an accuracy of|�z|/(1+z)� 1% and an outlier [with |�z|/(1 + z) > 0.15] fraction of � 1.4% for sources with spectroscopic redshifts. We performed blind tests to derive a more realistic estimate of the photo- z quality for sources without spectroscopic redshifts. We expect there are � 9% outliers for the relatively brighter sources ( R . 26), and the outlier fraction will increase to � 15‐25% for the fainter sources (R & 26). The typical photo-z accuracy is � 6‐7%. The outlier fraction and photo-z accuracy do not appear to have a redshift dependence (for z � 0‐4). These photo-z’s appear to be the best obtained so far for faint X-ray sources, an d they have been significantly ( & 50%) improved compared to previous estimates of the photo-z’s for the X-ra y sources in the � 2 Ms ChandraDeep Field-North and � 1 Ms ChandraDeep Field-South. Subject headings:cosmology: observations — galaxies: active — galaxies: distances and redshifts — galaxies: photometry — X-rays: galaxies

X-ray Binary Evolution Across Cosmic Time

High redshift galaxies permit the study of the formation and evolution of X-ray binary populations on cosmological timescales, probing a wide range of metallicitie s and star-formation rates. In this paper, we present results from a large scale population synthesis study that m odels the X-ray binary populations from the first galaxies of the universe until today. We use as input to our modeling the Millennium II Cosmological Simulation and the updated semi-analytic galaxy catalog by Guo et al. (2011) to self-consistently account for the star formation history and metallicity evolution of the uni verse. Our modeling, which is constrained by the observed X-ray properties of local galaxies, gives predict ions about the global scaling of emission from X-ray binary populations with properties such as star-formation rate and stellar mass, and the evolution of these relations with redshift. Our simulations show that the X-ray luminosity density (X-ray luminosity per unit volume) from X-ray binaries in our Universe today is dominated by low-mass X-ray binaries, and it is only at z & 2.5 that high-mass X-ray binaries become dominant. We also find t hat there is a delay of � 1.1 Gyr between the peak of X-ray emissivity from low-mass Xray binaries (at z � 2.1) and the peak of star-formation rate density (at z � 3.1). The peak of the X-ray luminosity from high-mass X-ray binaries (at z � 3.9), happens � 0.8 Gyr before the peak of the star-formation rate density, which is due to the metallicity evolution of the Universe. Subject headings:stars: binaries: close, stars: evolution, X-rays: binarie s, galaxies, diffuse background, galaxies: stellar content

SUPERMASSIVE BLACK HOLE GROWTH IN STARBURST GALAXIES OVER COSMIC TIME: CONSTRAINTS FROM THE DEEPEST CHANDRA FIELDS

We present an analysis of deep multiwavelength data for z 0.3-3 starburst galaxies selected by their 70 ?m emission in the Extended-Chandra Deep Field-South and Extended Groth Strip. We identify active galactic nuclei (AGNs) in these infrared sources through their X-ray emission and quantify the fraction that host an AGN. We find that the fraction depends strongly on both the mid-infrared color and rest-frame mid-infrared luminosity of the source, rising to ~50%-70% at the warmest colors (F 24 ?m/F 70 ?m 0.2) and highest mid-infrared luminosities (corresponding to ultraluminous infrared galaxies), similar to the trends found locally. Additionally, we find that the AGN fraction depends strongly on the star formation rate (SFR) of the host galaxy (inferred from the observed-frame 70 ?m luminosity after subtracting the estimated AGN contribution), particularly for more luminous AGNs (L 0.5 ? 8.0keV 1043?erg?s?1). At the highest SFRs (~1000 M ??yr?1), the fraction of galaxies with an X-ray detected AGN rises to 30%, roughly consistent with that found in high-redshift submillimeter galaxies. Assuming that the AGN fraction is driven by the SFR (rather than stellar mass or redshift, for which our sample is largely degenerate), this result implies that the duty cycle of luminous AGN activity increases with the SFR of the host galaxy: specifically, we find that luminous X-ray detected AGNs are at least ~5-10 times more common in systems with high SFRs ( 300 M ??yr?1) than in systems with lower SFRs ( 30 M ??yr?1). Lastly, we investigate the ratio between the supermassive black hole accretion rate (inferred from the AGN X-ray luminosity) and the bulge growth rate of the host galaxy (approximated as the SFR) and find that, for sources with detected AGNs and star formation (and neglecting systems with low star formation rates to which our data are insensitive), this ratio in distant starbursts agrees well with that expected from the local scaling relation assuming the black holes and bulges grew at the same epoch. These results imply that black holes and bulges grow together during periods of vigorous star formation and AGN activity.

THE X-RAY STAR FORMATION STORY AS TOLD BY LYMAN BREAK GALAXIES IN THE 4 Ms CDF-S

We present results from deep X-ray stacking of >4000 high redshift galaxies from z ≈1 to 8 using the 4 Ms Chandra Deep Field South (CDF-S) data, the deepest X-ray survey of the extragalactic sky to date. The galaxy samples were selected using the Lyman break technique based primarily on recent HST ACS and WFC3 observations. Based on such high specific star formation rates (sSFRs): log SFR/M∗ > −8.7, we expect that the observed properties of these LBGs are dominated by young stellar populations. The X-ray emission in LBGs, eliminating individually detected X-ray sources (potential AGN), is expected to be powered by X-ray binaries and hot gas. We find, for the first time, evidence of evolution in the X-ray/SFR relation. Based on X-ray stacking analyses for z < 4 LBGs (covering ∼ 90% of the Universe’s history), we find that the 2–10 keV X-ray luminosity evolves weakly with redshift (z) and SFR as: log LX = 0.93log(1+z)+0.65logSFR+39.80. By comparing our observations with sophisticated X-ray binary population synthesis models, we interpret that the redshift evolution of LX/SFR is driven by metallicity evolution in HMXBs, likely the dominant population in these high sSFR galaxies. We also compare these models with our observations of X-ray luminosity density (total 2–10 keV luminosity per Mpc 3 ) and find excellent agreement. While there are no significant stacked detections at z & 5, we use our upper limits from 5 . z . 8 LBGs to constrain the SMBH accretion history of the Universe around the epoch of reionization.

ENERGY FEEDBACK FROM X-RAY BINARIES IN THE EARLY UNIVERSE

X-ray photons, because of their long mean-free paths, can easily escape the galactic environments where they are produced, and interact at long distances with the intergalactic medium, potentially having a significant contribution to the heating and reionization of the early universe. The two most important sources of X-ray photons in the universe are active galactic nuclei (AGNs) and X-ray binaries (XRBs). In this Letter we use results from detailed, large scale population synthesis simulations to study the energy feedback of XRBs, from the first galaxies (z ∼ 20) until today. We estimate that X-ray emission from XRBs dominates over AGN at z ≳ 6-8. The shape of the spectral energy distribution of the emission from XRBs shows little change with redshift, in contrast to its normalization which evolves by ∼4 orders of magnitude, primarily due to the evolution of the cosmic star-formation rate. However, the metallicity and the mean stellar age of a given XRB population affect significantly its X-ray output. Specifically, the X-ray luminosity from high-mass XRBs per unit of star-formation rate varies an order of magnitude going from solar metallicity to less than 10% solar, and the X-ray luminosity from low-mass XRBs per unit of stellar mass peaks at an age of ∼300 Myr and then decreases gradually at later times, showing little variation for mean stellar ages ≳ 3 Gyr. Finally, we provide analytical and tabulated prescriptions for the energy output of XRBs, that can be directly incorporated in cosmological simulations.

X-ray emission from star-forming galaxies – III. Calibration of the LX-SFR relation up to redshift z ≈ 1.3

We investigate the relation between total X-ray emission from star-forming galaxies and their star formation activity. Using nearby late-type galaxies and ULIRGs from Paper I and star-forming galaxies from Chandra Deep Fields, we construct a sample of 66 galaxies spanning the redshift range z � 0 1.3 and the star-formation rate (SFR) range � 0.1 10 3 M⊙ yr −1 . In agreement with previous results, we find that the LX SFR relation is consistent with a linear law both at z = 0 and for the z = 0.1 1.3 CDF galaxies, within the statistical accuracy of � 0.1 in the slope of the LX SFR relation. For the total sample, we find a linear scaling relation LX/SFR � (4.0 ± 0.4)× 10 39 (ergs −1 )/(M⊙ yr −1 ), with a scatter of � 0.4 dex. About � 2/3 of the 0.5–8 keV luminosity generated per unit SFR is expected to be due to HMXBs. We find no statistically significant trends in the mean LX/SFR ratio with the redshift or star formation rate and constrain the amplitude of its variations by . 0.1 0.2 dex. These properties make X-ray observations a powerful tool to measure the star formation rate in normal star-forming galaxies that dominate the source counts at faint fluxes.