The 4 Ms Chandra Deep Field-South number counts apportioned by source class : pervasive active galactic nuclei and the ascent of normal galaxies

We present 0.5-2 keV, 2-8 keV, 4-8 keV, and 0.5-8 keV (hereafter soft, hard, ultra-hard, and full bands, respectively) cumulative and differential number-count (log N-log S) measurements for the recently completed ≈4 Ms Chandra Deep Field-South (CDF-S) survey, the deepest X-ray survey to date. We implement a new Bayesian approach, which allows reliable calculation of number counts down to flux limits that are factors of ≈1.9-4.3 times fainter than the previously deepest number-count investigations. In the soft band (SB), the most sensitive bandpass in our analysis, the ≈4 Ms CDF-S reaches a maximum source density of ≈27,800 deg-2. By virtue of the exquisite X-ray and multiwavelength data available in the CDF-S, we are able to measure the number counts from a variety of source populations (active galactic nuclei (AGNs), normal galaxies, and Galactic stars) and subpopulations (as a function of redshift, AGN absorption, luminosity, and galaxy morphology) and test models that describe their evolution. We find that AGNs still dominate the X-ray number counts down to the faintest flux levels for all bands and reach a limiting SB source density of ≈14,900 deg-2, the highest reliable AGN source density measured at any wavelength. We find that the normal-galaxy counts rise rapidly near the flux limits and, at the limiting SB flux, reach source densities of ≈12,700 deg-2 and make up 46% ± 5% of the total number counts. The rapid rise of the galaxy counts toward faint fluxes, as well as significant normal-galaxy contributions to the overall number counts, indicates that normal galaxies will overtake AGNs just below the ≈4 Ms SB flux limit and will provide a numerically significant new X-ray source population in future surveys that reach below the ≈4 Ms sensitivity limit. We show that a future ≈10 Ms CDF-S would allow for a significant increase in X-ray-detected sources, with many of the new sources being cosmologically distant (z >~ 0.6) normal galaxies

X-ray Survey Results on Active Galaxy Physics and Evolution

This "pedagogical" review describes the key Chandra and XMM-Newton extragalactic surveys to date and details some of their implications for AGN physics and evolution. We additionally highlight two topics of current widespread interest: (1) X-ray constraints on the AGN content of luminous submillimeter galaxies, and (2) the demography and physics of high-redshift (z > 4) AGN as revealed by X-ray observations. Finally, we discuss prospects for future X-ray surveys with Chandra, XMM-Newton, and upcoming missions.Comment: 26 pages, in Physics of Active Galactic Nuclei at All Scales, eds. Alloin D., Johnson R., Lira P. (Springer-Verlag, Berlin), version with all figures at http://www.astro.psu.edu/users/niel/papers/papers.htm

X-ray Spectroscopy and Variability of AGN Detected in the 2 Ms Chandra Deep Field-North Survey

We investigate the nature of the faint X-ray source population through X-ray spectroscopy and variability analyses of 136 AGN detected in the 2 Ms Chandra Deep Field-North survey with > 200 background-subtracted 0.5-8.0 keV counts [F(0.5-8.0 keV)=(1.4-200)e-15 erg cm^{-2} s^{-1}]. Our preliminary spectral analyses yield median spectral parameters of Gamma=1.61 and intrinsic N_H=6.2e21 cm^{-2} (z=1 assumed when no redshift available) when the AGN spectra are fitted with a simple absorbed power-law model. However, considerable spectral complexity is apparent (e.g., reflection, partial covering) and must be taken into account to model the data accurately. Moreover, the choice of spectral model (i.e., free vs. fixed photon index) has a pronounced effect on the derived N_H distribution and, to a lesser extent, the X-ray luminosity distribution. Ten of the 136 AGN (~7%) show significant Fe Kalpha emission-line features with equivalent widths in the range 0.1-1.3 keV. Two of these emission-line AGN could potentially be Compton thick (i.e., Gamma < 1.0 and large Fe Kalpha equivalent width). Finally, we find that 81 (~60%) of the 136 AGN show signs of variability, and that this fraction increases significantly (~80-90%) when better photon statistics are available.Comment: Submitted to Advances in Space Research for New X-ray Results from Clusters of Galaxies and Black Holes (Oct 2002; Houston, TX), eds. C. Done, E.M. Puchnarewicz, M.J. Ward. Requires cospar.sty (6 pgs, 10 figs

Uncovering the Near-IR Dwarf Galaxy Population of the Coma Cluster with Spitzer IRAC

We present the first results of a Spitzer IRAC (Infrared Array Camera) wide-field survey of the Coma cluster. The observations cover two fields of different galaxy densities; the first is a 0.733 deg^2 region in the core of the cluster (Coma 1), the second a 0.555 deg^2 off-center region located ~57 arcmin (1.7 Mpc) south-west from the core (Coma 3). The observations, although short 70-90 s exposures, are very sensitive; we detect ~29,200 sources at 3.6 micron over the total ~1.3 deg^2 survey area. We construct 3.6 micron galaxy luminosity functions (LFs) for each field using selection functions based on spectroscopic redshifts. At the bright end, the LFs are well modeled by a traditional Schechter function; [M^star (3.6 micron), alpha_1] = [-25.17, -1.18] and [-24.69, -1.30] for Coma 1 and Coma 3 respectively. However, at the faint end (M(3.6 micron) > -20.5), there is a steep increase in the LF slope in both fields indicative of large numbers of red dwarf galaxies. The reality of this population is examined using optical counterparts in SDSS data with optical color filtering (g-r<1.3). The steep increase can be modeled with a power-law function, with slopes of alpha_2 = -2.18 (Coma 1) and alpha_2 = -2.60 (Coma 3). A qualitative comparison with optical (B- and R-band) LFs shows that we are likely to be observing a larger population of dwarf galaxies in the near-IR, which may be a low-surface-brightness (LSB) population that IRAC is particularly sensitive to, or a population too red to be detected in existing optical surveys down to R~20.Comment: 18 pages, 15 figures. Accepted for publication in ApJ. Typos corrected and minor updates to Table 4/Fig.15 to match proofed versio

The Chandra Deep Field North Survey. VI. The nature of the optically faint X-ray source population

We provide constraints on the nature of the optically faint (I 24) X-ray source population from a 1 Ms Chandra exposure of a 84 × 84 region within the Hawaii flanking-field area containing the Hubble Deep Field North region. We detect 47 (2400 deg-2) optically faint sources down to 0.52.0 keV and 2.08.0 keV fluxes of 3 × 10-17 ergs cm-2 s-1 and 2 × 10-16 ergs cm-2 s-1, respectively; these sources contribute 14% and 21% of the 0.52.0 keV and 2.08.0 keV X-ray background radiation, respectively. The fraction of optically faint X-ray sources is approximately constant (at 35%) for 0.58.0 keV fluxes from 3 × 10-14 ergs cm-2 s-1 down to the X-ray flux limit. A considerable fraction (30%) of the optically faint X-ray sources are Very Red Objects (I-K 4). Analysis of the optical and X-ray properties suggests a large number of optically faint X-ray sources are likely to host obscured active galactic nucleus (AGN) activity at z = 13. From these results we calculate that a significant fraction (5%45%) of the optically faint X-ray source population could be obscured QSOs (rest-frame unabsorbed 0.58.0 keV luminosity >3 × 1044 ergs s-1) at z 3. Given the number of X-ray sources without I-band counterparts, there are unlikely to be more than 15 sources at z > 6. We provide evidence that the true number of z > 6 sources is considerably lower. We investigate the multiwavelength properties of optically faint X-ray sources. Nine optically faint X-ray sources have Jy radio counterparts; 53% of the optically faint Jy radio sources in this region. The most likely origin of the X-ray emission in these X-ray detected, optically faint Jy radio sources is obscured AGN activity. However, two of these sources have been previously detected at submillimeter wavelengths, and the X-ray emission from these sources could be due to luminous star formation activity. Assuming the spectral energy distribution of NGC 6240, we estimate the 175 m flux of a typical optically faint X-ray source to be less than 10 mJy; however, those sources with detectable submillimeter counterparts (i.e., f850 m > 3 mJy) could be substantially brighter. Hence, most optically faint X-ray sources are unlikely to contribute significantly to the far-IR (140240 m) background radiation. However, as expected for sources with AGN activity, the two optically faint X-ray sources within the most sensitive area of the ISOCAM HDF-N region have faint (50 Jy) 15 m counterparts. We also provide constraints on the average X-ray properties of classes of optically faint sources not individually detected at X-ray energies. Stacking analyses of optically faint Jy radio sources not individually detected with X-ray emission yields a possible detection (at 98.3% confidence) in the 0.52.0 keV band; this X-ray emission could be produced by star formation activity at z = 13. None of the optically faint AGN-candidate sources in the HDF-N itself are detected at X-ray energies either individually or with stacking analyses, showing that these sources have low X-ray luminosities if they are indeed AGNs

The Properties and Redshift Evolution of Intermediate-Luminosity Off-Nuclear X-Ray Sources in the Chandra Deep Fields

We analyze a population of intermediate-redshift (z~0.05-0.3) off-nuclear X-ray sources located within optically bright galaxies in the Great Observatories Origins Deep Survey and Galaxy Evolution from Morphology and SEDs fields. A total of 24 off-nuclear source candidates are classified using deep Chandra X-Ray Observatory exposures from the Chandra Deep Field-North, Chandra Deep Field-South, and Extended Chandra Deep Field-South 15 of these are newly identified. These sources have average X-ray spectral shapes and optical environments similar to those observed for off-nuclear intermediate-luminosity (LX>=1039 ergs s-1 in the 0.5-2.0 keV band) X-ray objects (IXOs; sometimes referred to as ultraluminous X-ray sources) in the local universe. This sample improves the available source statistics for intermediate-redshift off-nuclear sources with LX>~1039.5 ergs s-1, and it places significant new constraints on the redshift evolution of the off-nuclear source frequency in field galaxies. The fraction of intermediate-redshift field galaxies containing an off-nuclear source with LX>~1039 ergs s-1 is suggestively elevated (~80% confidence level) with respect to that observed for IXOs in the local universe; we calculate this elevation to be a factor of ~1.9+1.4-1.3. A rise in this fraction is plausibly expected as a consequence of the observed increase in global star formation density with redshift, and our results are consistent with the expected magnitude of the rise in this fraction

Concurrent supermassive black hole and galaxy growth : linking environment and nuclear activity in z = 2.23 H-alpha emitters

We present results from a ≈100 ks Chandra observation of the 2QZ Cluster 1004+00 structure at z = 2.23 (hereafter 2QZ Clus). 2QZ Clus was originally identified as an overdensity of four optically-selected QSOs at z = 2.23 within a 15 × 15 arcmin2 region. Narrow-band imaging in the near-IR (within the K band) revealed that the structure contains an additional overdensity of 22 z = 2.23 Hα-emitting galaxies (HAEs), resulting in 23 unique z = 2.23 HAEs/QSOs (22 within the Chandra field of view). Our Chandra observations reveal that three HAEs in addition to the four QSOs harbor powerfully accreting supermassive black holes (SMBHs), with 2-10 keV luminosities of ≈(8-60) × 1043 erg s-1 and X-ray spectral slopes consistent with unobscured active galactic nucleus (AGN). Using a large comparison sample of 210 z = 2.23 HAEs in the Chandra-COSMOS field (C-COSMOS), we find suggestive evidence that the AGN fraction increases with local HAE galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment (a factor of ≈2 times over the field), and after excluding optically-selected QSOs, we find that the AGN fraction is a factor of ≈3.5+3.8 -2.2 times higher than C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra data and Herschel SPIRE observations at 250 μm, we respectively estimate mean SMBH accretion rates (\dot{M}_BH) and star formation rates (SFRs) for the 2QZ Clus and C-COSMOS samples. We find that the mean 2QZ Clus HAE stacked X-ray luminosity is QSO-like (L 2-10 keV ≈ [6-10] × 1043 erg s-1), and the implied \dot{M}_BH/SFR ≈ (1.6-3.2) × 10-3 is broadly consistent with the local M BH/M sstarf relation and z ≈ 2 X-ray selected AGN. In contrast, the C-COSMOS HAEs are on average an order of magnitude less X-ray luminous and have \dot{M}_BH/SFR ≈ (0.2-0.4) × 10-3, somewhat lower than the local M BH/M sstarf relation, but comparable to that found for z ≈ 1-2 star-forming galaxies with similar mean X-ray luminosities. We estimate that a periodic QSO phase with duty cycle ≈2%-8% would be sufficient to bring star-forming galaxies onto the local M BH/M sstarf relation. This duty cycle is broadly consistent with the observed C-COSMOS HAE AGN fraction (≈0.4%-2.3%) for powerful AGN with L X >~ 1044 erg s-1. Future observations of 2QZ Clus will be needed to identify key factors responsible for driving the mutual growth of the SMBHs and galaxies

The Chandra Deep Field North Survey. XIII. 2 Ms point-source catalogs

We present point-source catalogs for the 2 Ms exposure of the Chandra Deep Field North, currently the deepest X-ray observation of the universe in the 0.58.0 keV band. Five hundred and three (503) X-ray sources are detected over an 448 arcmin2 area in up to seven X-ray bands. Twenty (20) of these X-ray sources lie in the central 5.3 arcmin2 Hubble Deep Field North (13,600 sources deg-2). The on-axis sensitivity limits are 2.5 × 10-17 ergs cm-2 s-1 (0.52.0 keV) and 1.4 × 10-16 ergs cm-2 s-1 (28 keV). Source positions are determined using matched-filter and centroiding techniques; the median positional uncertainty is 03. The X-ray colors of the detected sources indicate a broad variety of source types, although absorbed AGNs (including a small number of possible Compton-thick sources) are clearly the dominant type. We also match lower significance X-ray sources to optical counterparts and provide a list of 79 optically bright (R 23) lower significance Chandra sources. The majority of these sources appear to be starburst and normal galaxies. The average backgrounds in the 0.52.0 keV and 28 keV bands are 0.056 and 0.135 counts Ms-1 pixel-1, respectively. The background count distributions are very similar to Poisson distributions. We show that this 2 Ms exposure is approximately photon limited in all seven X-ray bands for regions close to the aim point, and we predict that exposures up to 25 Ms (0.52.0 keV) and 4 Ms (28 keV) should remain nearly photon limited. We demonstrate that this observation does not suffer from source confusion within 6 of the aim point, and future observations are unlikely to be source-confusion limited within 3 of the aim point even for source densities exceeding 100,000 deg-2. These analyses directly show that Chandra can achieve significantly higher sensitivities in an efficient, nearly photon-limited manner and be largely free of source confusion. To allow consistent comparisons, we have also produced point-source catalogs for the 1 Ms Chandra Deep Field South (CDF-S). Three hundred and twenty-six (326) X-ray sources are included in the main Chandra catalog, and an additional 42 optically bright X-ray sources are included in a lower significance Chandra catalog. We find good agreement with the photometry of the previously published CDF-S catalogs; however, we provide significantly improved positional accuracy