We present a measure of the hard (2-8 keV) X-ray luminosity function (XLF) of AGNs up to image. At high redshifts, the wide area coverage of the Chandra Multiwavength Project is crucial to detect ...rare and luminous AGNs. The inclusion of samples from deeper published surveys, such as the Chandra Deep Fields, allows us to span the lower L sub(X) range of the XLF. Our sample is selected from both the hard and soft energy band detections. Within our optical magnitude limits, we achieve an adequate level of completeness (>50%) regarding X-ray source identification (i.e., redshift). We find that the luminosity function is similar to that found in previous X- ray surveys up to image with an evolution dependent on both luminosity and redshift. At image, there is a significant decline in the numbers of AGNs with an evolution rate similar to that found by studies of optically selected QSOs. Based on our XLF, we assess the resolved fraction of the cosmic X-ray background, the cumulative mass density of SMBHs, and the comparison of the mean accretion rate onto SMBHs and the star formation history of galaxies as a function of redshift. A coevolution scenario up to image is plausible, although at higher redshifts the accretion rate onto SMBHs drops more rapidly. Finally, we highlight the need for better statistics of high- redshift AGNs at image, which is achievable with the upcoming Chandra surveys.
The Blanco Cosmology Survey (BCS) is a 60 night imaging survey of ~80 deg super(2) of the southern sky located in two fields: (alpha, delta) = (5 hr, -55degrees) and (23 hr, -55degrees). The survey ...was carried out between 2005 and 2008 in griz bands with the Mosaic2 imager on the Blanco 4 m telescope. The primary aim of the BCS survey is to provide the data required to optically confirm and measure photometric redshifts for Sunyaev-Zel'dovich effect selected galaxy clusters from the South Pole Telescope and the Atacama Cosmology Telescope. We process and calibrate the BCS data, carrying out point-spread function-corrected model-fitting photometry for all detected objects. The median 10sigma galaxy (point-source) depths over the survey in griz are approximately 23.3 (23.9), 23.4 (24.0), 23.0 (23.6), and 21.3 (22.1), respectively. The astrometric accuracy relative to the USNO-B survey is ~45 mas. We calibrate our absolute photometry using the stellar locus in grizJ bands, and thus our absolute photometric scale derives from the Two Micron All Sky Survey, which has ~2% accuracy. The scatter of stars about the stellar locus indicates a systematic floor in the relative stellar photometric scatter in griz that is ~1.9%, ~2.2%, ~2.7%, and ~2.7%, respectively. A simple cut in the AstrOmatic star-galaxy classifier spread_model produces a star sample with good spatial uniformity. We use the resulting photometric catalogs to calibrate photometric redshifts for the survey and demonstrate scatter deltaz/(1 + z) = 0.054 with an outlier fraction eta < 5% to z ~ 1. We highlight some selected science results to date and provide a full description of the released data products.
We report the discovery of two ultra-faint stellar systems found in early data from the DECam Local Volume Exploration survey (DELVE). The first system, Centaurus I (DELVE J1238-4054), is identified ...as a resolved overdensity of old and metal-poor stars with a heliocentric distance of , a half-light radius of , an age of , a metallicity of , and an absolute magnitude of . This characterization is consistent with the population of ultra-faint satellites and confirmation of this system would make Centaurus I one of the brightest recently discovered ultra-faint dwarf galaxies. Centaurus I is detected in Gaia DR2 with a clear and distinct proper motion signal, confirming that it is a real association of stars distinct from the Milky Way foreground; this is further supported by the clustering of blue horizontal branch stars near the centroid of the system. The second system, DELVE 1 (DELVE J1630-0058), is identified as a resolved overdensity of stars with a heliocentric distance of , a half-light radius of , an age of , a metallicity of , and an absolute magnitude of , consistent with the known population of faint halo star clusters. Given the low number of probable member stars at magnitudes accessible with Gaia DR2, a proper motion signal for DELVE 1 is only marginally detected. We compare the spatial position and proper motion of both Centaurus I and DELVE 1 with simulations of the accreted satellite population of the Large Magellanic Cloud (LMC) and find that neither is likely to be associated with the LMC.
We present the Chandra Multiwavelength Project (ChaMP) X-ray point source catalog with 66800 X-ray sources detected in 149 Chandra observations covering 610 deg super(2). The full ChaMP catalog ...sample is 7 times larger than the initial published ChaMP catalog. The exposure time of the fields in our sample ranges from 0.9 to 124 ks, corresponding to a deepest X-ray flux limit of f sub(0.5-8.0) = 9 x 10 super(-16) ergs cm super(-2) s super(-1). The ChaMP X-ray data have been uniformly reduced and analyzed with ChaMP-specific pipelines and then carefully validated by visual inspection. The ChaMP catalog includes X-ray photometric data in eight different energy bands as well as X-ray spectral hardness ratios and colors. To best utilize the ChaMP catalog, we also present the source reliability, detection probability, and positional uncertainty. To quantitatively assess those parameters, we performed extensive simulations. In particular, we present a set of empirical equations: the flux limit as a function of effective exposure time and the positional uncertainty as a function of source counts and off-axis angle. The false source detection rate is 61% of all detected ChaMP sources, while the detection probability is better than 695% for sources with counts 30 and off-axis angle < 5'. The typical positional offset between ChaMP X-ray source and their SDSS optical counterparts is 0.7" c 0.4", derived from 6900 matched sources.
We present the Chandra Multiwavelength Project (ChaMP) X-ray point source number counts and cosmic X-ray background (CXRB) flux densities in multiple energy bands. From the ChaMP X-ray point source ...catalog, similar to 5500 sources are selected, covering 9.6 deg super(2) in sky area. To quantitatively characterize the sensitivity and completeness of the ChaMP sample, we perform extensive simulations. We also include the ChaMP+CDFs (Chandra Deep Fields) number counts to cover large flux ranges from 2 x 10 super(-17) to 2.4 x 10 super(-12) (0.5-2 keV) and from 2 x 10 super(-16) to 7.1 x 10 super(-12) (2-8 keV) ergs cm super(-2) s super(-1). The ChaMP and the ChaMP+CDFs differential number counts are well fitted with a broken power law. The best-fit faint and bright power indices are 1.49 plus or minus 0.02 and 2.36 plus or minus 0.05 (0.5-2 keV), and 1.58 plus or minus 0.01 and 2.59 super(+) sub(-) super(0) sub(0) super(.) sub(.) super(0) sub(0) super(6) sub(5) (2-8 keV), respectively. We detect breaks in the differential number counts that appear at different fluxes in different energy bands. Assuming a single power-law model for a source spectrum, we find that the same population(s) of soft X-ray sources causes the break in the differential number counts for all energy bands. We measure the resolved CXRB flux densities from the ChaMP and the ChaMP+CDFs number counts with and without bright target sources. By adding the known unresolved CXRB to the ChaMP+CDF resolved CXRB, we also estimate total CXRB flux densities. The fractions of the resolved CXRB without target sources are 78% plus or minus 1% and 81% plus or minus 2% in the 0.5-2 and 2-8 keV bands, respectively, somewhat lower than but generally consistent with earlier numbers because of their large errors. These fractions increase by plus or minus 1% when target sources are included.
ABSTRACT
The Vera C. Rubin Observatory Legacy Survey of Space and Time (LSST) will observe several Deep Drilling Fields (DDFs) to a greater depth and with a more rapid cadence than the main survey. ...In this paper, we describe the ‘DeepDrill’ survey, which used the Spitzer Space Telescope Infrared Array Camera (IRAC) to observe three of the four currently defined DDFs in two bands, centred on 3.6 and 4.5 μm. These observations expand the area that was covered by an earlier set of observations in these three fields by the Spitzer Extragalactic Representative Volume Survey (SERVS). The combined DeepDrill and SERVS data cover the footprints of the LSST DDFs in the Extended Chandra Deep Field–South (ECDFS) field, the ELAIS-S1 field (ES1), and the XMM-Large-Scale Structure Survey field (XMM-LSS). The observations reach an approximate 5σ point-source depth of 2 μJy (corresponding to an AB magnitude of 23.1; sufficient to detect a 10$^{11} \, \mathrm{M}_{\odot}$ galaxy out to z ≈ 5) in each of the two bands over a total area of $\approx 29\,$ deg2. The dual-band catalogues contain a total of 2.35 million sources. In this paper, we describe the observations and data products from the survey, and an overview of the properties of galaxies in the survey. We compare the source counts to predictions from the Shark semi-analytic model of galaxy formation. We also identify a population of sources with extremely red (3.6−4.5 >1.2) colours which we show mostly consists of highly obscured active galactic nuclei.
We present the results from a survey of 57 low-redshift Abell galaxy dusters to study the radial dependence of the luminosity function (LF). The dynamical radius of each cluster, r sub(200), was ...estimated from the photometric measurement of cluster richness, Bgc. The shape of the LFs is found to correlate with radius such that the faint-end slope, alpha , is generally steeper on the cluster outskirts. The sum of two Schechter functions provides a more adequate fit to the composite LFs than a single Schechter function. LFs based on the selection of red and blue galaxies are bimodal in appearance. The red LFs are generally flat for -22 less than or equal to M sub(RC) less than or equal to -18, with a radius-dependent steepening of alpha for M sub(RC) > -18. The blue LFs contain a larger contribution from faint galaxies than the red LFs. The blue LFs have a rising faint-end component ( alpha similar to -1.7) for M sub(RC) > -21, with a weaker dependence on radius than the red LFs. The dispersion of M* was determined to be 0.31 mag, which is comparable to the median measurement uncertainty of 0.38 mag. This suggests that the bright end of the LF is universal in shape at the 0.3 mag level. We find that M* is not correlated with cluster richness when using a common dynamical radius. Also, we find that M* is weakly correlated with BM type such that later BM-type clusters have a brighter M*. A correlation between M* and radius was found for the red and blue galaxies such that M* fades toward the cluster center.
We study the spectral energy distributions and evolution of a large sample of optically selected quasars from the Sloan Digital Sky Survey that were observed in 323 Chandra images analyzed by the ...Chandra Multiwavelength Project. Our highest-confidence matched sample includes 1135 X-ray detected quasars in the redshift range 0.2 < z < 5.4, representing some 36 Msec of effective exposure. We provide catalogs of QSO properties, and describe our novel method of calculating X-ray flux upper limits and effective sky coverage. Spectroscopic redshifts are available for about 1/3 of the detected sample; elsewhere, redshifts are estimated photometrically. We detect 56 QSOs with redshift z > 3, substantially expanding the known sample. We find no evidence for evolution out to z ~ 5 for either the X-ray photon index Gamma or for the ratio of optical/UV to X-ray flux alpha ox. About 10% of detected QSOs show best-fit intrinsic absorbing columns greater than 1022 cm-2, but the fraction might reach ~1/3 if most nondetections are absorbed. We confirm a significant correlation between alpha ox and optical luminosity, but it flattens or disappears for fainter (MB -23) active galactic nucleus (AGN) alone. We report significant hardening of Gamma both toward higher X-ray luminosity, and for relatively X-ray loud quasars. These trends may represent a relative increase in nonthermal X-ray emission, and our findings thereby strengthen analogies between Galactic black hole binaries and AGN. For uniformly selected subsamples of narrow-line Seyfert 1s and narrow absorption line QSOs, we find no evidence for unusual distributions of either alpha ox or Gamma .
We have found that the brightest cluster galaxy (BCG) in A85, Holm 15A, displays the largest core known so far. Its cusp radius, r sub(gamma) = 4.57 + or - 0.06 kpc (4."26 + or - 0."06), is more than ...18 times larger than the mean for BCGs and > ~ 1 kpc larger than A2261-BCG, hitherto the largest-cored BCG. Holm 15A hosts the luminous amorphous radio source 0039-095B and has the optical signature of a LINER. Scaling laws indicate that this core could host a supermassive black hole (SMBH) of mass M sub(bullet) ~ (10 super(9)-10 super(11)) M sub(middot in circle). We suggest that cores this large represent a relatively short phase in the evolution of BCGs, whereas the masses of their associated SBMH might be set by initial conditions.
For measurement of the active galactic nucleus (AGN) luminosity function and its evolution, X-ray selection samples all types of AGNs and provides reduced obscuration bias in comparison with UV ...excess or optical surveys. The apparent decline in optically selected quasars above z 6 3 may be strongly affected by such a bias. The Chandra Multiwavelength Project (CHAMP) is characterizing serendipitously detected X-ray sources in a large number of fields with archival Chandra imaging. We present a preliminary measure of the comoving space density using a sample of 311 AGNs found in 23 CHAMP fields (61.8 deg super(2)) supplemented with 57 X-ray-bright AGNs from the Chandra Deep Field-North and Chandra Deep Field-South. Within our X-ray flux (f sub(0.3-8.0 keV) > 4 x 10 super(-15) ergs cm super(-2) s super(-1)) and optical magnitude (r < 22.5) limits, our sample includes 14 broad emission-line AGNs at z > 3. Using this X-ray-selected sample, we detect a turnover in the comoving space density of luminous type 1 AGNs (log L sub(X) > 44.5 ergs s super(-1), measured in the 0.3-8.0 keV band and corrected for Galactic absorption) at z > 2.5. Our X-ray sample is the first to show a behavior similar to the well-established evolution of the optical quasar luminosity function. A larger sample of high-redshift AGNs and with a greater fraction of identified sources, either spectroscopic or photometric, at faint optical magnitudes (r > 22.5) are required to remove the remaining uncertainty in our measure of the X-ray luminosity function, particularly given the possibility that AGNs might be more easily obscured optically at high redshift. We confirm that for z < 1, lower luminosity AGNs (log L sub(X) < 44.5) are more prevalent by more than an order of magnitude than those with high luminosity. We have combined the Chandra sample with AGNs from the ROSAT surveys to present a measure of the space density of luminous type 1 AGNs in the soft X-ray band (0.5-2.0 keV) that confirms the broadband turnover described above.
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