- ID:
- ivo://CDS.VizieR/J/ApJS/184/158
- Title:
- Chandra COSMOS survey I.
- Short Name:
- J/ApJS/184/158
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Chandra COSMOS Survey (C-COSMOS) is a large, 1.8Ms, Chandra program that has imaged the central 0.5deg^2^ of the COSMOS field (centered at 10h, +02d) with an effective exposure of ~160ks, and an outer 0.4deg^2^ area with an effective exposure of ~80ks. The limiting source detection depths are 1.9x10^-16^erg/cm2/s in the soft (0.5-2keV) band, 7.3x10^-16^erg/cm2/s in the hard (2-10keV) band, and 5.7x10^-16^erg/cm2/s in the full (0.5-10keV) band. Here we describe the strategy, design, and execution of the C-COSMOS survey, and present the catalog of 1761 point sources detected at a probability of being spurious of <2x10^-5^ (1655 in the full, 1340 in the soft, and 1017 in the hard bands). By using a grid of 36 heavily (~50%) overlapping pointing positions with the ACIS-I imager, a remarkably uniform (+/-12%) exposure across the inner 0.5deg^2^ field was obtained, leading to a sharply defined lower flux limit. The widely different point-spread functions obtained in each exposure at each point in the field required a novel source detection method, because of the overlapping tiling strategy, which is described in a companion paper. This method produced reliable sources down to a 7-12 counts, as verified by the resulting logN-logS curve, with subarcsecond positions, enabling optical and infrared identifications of virtually all sources, as reported in a second companion paper.
Number of results to display per page
Search Results
- ID:
- ivo://CDS.VizieR/J/AJ/122/2810
- Title:
- Chandra Deep Field North Survey. V.
- Short Name:
- J/AJ/122/2810
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- An extremely deep X-ray survey (~1Ms) of the Hubble Deep Field North (HDF-N) and its environs (~450arcmin^2^) has been performed with the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory. This is one of the two deepest X-ray surveys ever performed; for point sources near the aim point, it reaches 0.5-2.0 and 2-8keV flux limits of ~3x10^-17^ and ~2x10^-16^ergs/cm^2^/s, respectively. Here we provide source catalogs, along with details of the observations, data reduction, and technical analysis. Observing conditions, such as background, were excellent for almost all of the exposure. We have detected 370 distinct point sources: 360 in the 0.5-8.0keV band, 325 in the 0.5-2.0keV band, 265 in the 2-8keV band, and 145 in the 4-8keV band. Two new Chandra sources in the HDF-N itself are reported and discussed. Source positions are accurate to within 0.6"-1.7" (at ~90% confidence), depending mainly on the off-axis angle. We also detect two highly significant extended X-ray sources and several other likely extended X-ray sources. We present basic number count results for sources located near the center of the field. Source densities of 7100^+1100^_-940_deg^-2^ (at 4.2x10^-17^ergs/cm^2^/s) and 4200^+670^_580_deg^-2^ (at 3.8x10^-16^ergs/cm^2^/s) are observed in the soft and hard bands, respectively.
- ID:
- ivo://CDS.VizieR/J/AJ/124/2351
- Title:
- Chandra Deep Field North survey. XII
- Short Name:
- J/AJ/124/2351
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We investigate the relationship between faint X-ray and 1.4GHz radio source populations detected within 3' of the Hubble Deep Field (North) using the 1Ms Chandra (Cat. <J/AJ/122/2810>) and 40{mu}Jy VLA (Cat. <J/ApJ/533/611>) surveys. Within this region, we find that ~42% of the 62 X-ray sources have radio counterparts and ~71% of the 28 radio sources have X-ray counterparts; thus, a 40{mu}Jy VLA survey at 1.4GHz appears to be well matched to a 1Ms Chandra observation.
- ID:
- ivo://CDS.VizieR/J/ApJS/139/369
- Title:
- Chandra Deep Field South. 1 Ms catalog
- Short Name:
- J/ApJS/139/369
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper we present the source catalog obtained from a 942ks exposure of the Chandra Deep Field South (CDFS), using the Advanced CCD Imaging Spectrometer (ACIS-I) on the Chandra X-ray Observatory. Eleven individual pointings made between 1999 October and 2000 December were combined to generate the final image used for object detection. Catalog generation proceeded simultaneously using two different methods: a method of our own design using a modified version of the SExtractor algorithm, and a wavelet transform technique developed specifically for Chandra observations. The detection threshold has been set in order to have less than 10 spurious sources, as assessed by extensive simulations. We subdivided the catalog into four sections: the primary list consisting of objects common to the two detection methods, two secondary lists containing sources which were detected by (1) the SExtractor algorithm alone and (2) the wavelet technique alone, and the fourth list consisting of possible diffuse or extended sources. The flux limits at the aimpoint for the soft (0.5-2keV) and hard (2-10keV) bands are 5.5x10^-17^erg/s/cm^2^ and 4.5x10^-16^erg/s/cm^2^, respectively. The total number of sources is 346; out of them, 307 were detected in the 0.5-2keV band, and 251 in the 2-10keV band. We also present optical identifications for the catalogued sources. Our primary optical data are R band imaging from VLT/FORS1 to a depth of R~26.5 (Vega). In regions of the field not covered by the VLT/FORS1 deep imaging, we use R-band data obtained with the Wide Field Imager (WFI) on the ESO-MPI 2.2 m telescope, as part of the ESO Imaging Survey (EIS), which cover the entire X-ray survey. We found that the FORS1/Chandra offsets are small, ~1". Coordinate cross-correlation finds 85% of the Chandra sources covered by FORS1 R to have counterparts within the 3{sigma} error box (>~1.5" depending on off-axis angle and X-ray signal-to-noise). The unidentified fraction of sources, approximately ~10%-15%, is close to the limit expected from the observed X-ray flux to R-band ratio distribution for the identified sample.
- ID:
- ivo://CDS.VizieR/J/ApJS/155/271
- Title:
- Chandra Deep Field-South: Optical spectroscopy
- Short Name:
- J/ApJS/155/271
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our spectroscopic follow-up program of the X-ray sources detected in the 942ks exposure of the Chandra Deep Field-South (CDFS). A total of 288 possible counterparts were observed at the VLT with the FORS1/FORS2 spectrographs for 251 of the 349 Chandra sources (including three additional faint X-ray sources). Spectra and R-band images are shown for all the observed sources and R-K colors are given for most of them. Spectroscopic redshifts were obtained for 168 X-ray sources, of which 137 have both reliable optical identification and redshift estimate (including 16 external identifications). The R<24 observed sample comprises 161 X-ray objects (181 optical counterparts), and 126 of them have unambiguous spectroscopic identification.
- ID:
- ivo://CDS.VizieR/J/ApJS/228/2
- Title:
- Chandra Deep Field-South survey: 7Ms sources
- Short Name:
- J/ApJS/228/2
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present X-ray source catalogs for the ~7Ms exposure of the Chandra Deep Field-South (CDF-S), which covers a total area of 484.2arcmin^2^. Utilizing wavdetect for initial source detection and ACIS Extract for photometric extraction and significance assessment, we create a main source catalog containing 1008 sources that are detected in up to three X-ray bands: 0.5-7.0keV, 0.5-2.0keV, and 2-7keV. A supplementary source catalog is also provided, including 47 lower-significance sources that have bright (K_s_<=23) near-infrared counterparts. We identify multiwavelength counterparts for 992 (98.4%) of the main-catalog sources, and we collect redshifts for 986 of these sources, including 653 spectroscopic redshifts and 333 photometric redshifts. Based on the X-ray and multiwavelength properties, we identify 711 active galactic nuclei (AGNs) from the main-catalog sources. Compared to the previous ~4Ms CDF-S catalogs, 291 of the main-catalog sources are new detections. We have achieved unprecedented X-ray sensitivity with average flux limits over the central ~1arcmin^2^ region of ~1.9x10^-17^, 6.4x10^-18^, and 2.7x10^-17^erg/cm^2^/s in the three X-ray bands, respectively. We provide cumulative number-count measurements observing, for the first time, that normal galaxies start to dominate the X-ray source population at the faintest 0.5-2.0keV flux levels. The highest X-ray source density reaches ~50500deg^-2^, and 47%+/-4% of these sources are AGNs (~23900deg^-2^).
- ID:
- ivo://CDS.VizieR/J/MNRAS/400/299
- Title:
- Chandra deep protocluster survey
- Short Name:
- J/MNRAS/400/299
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present X-ray point-source catalogues for a deep ~400ks Chandra ACIS-I (Advanced CCD Imaging Spectrometer) exposure of the SSA22 field. The observations are centred on a z=3.09 protocluster, which is populated by Lyman break galaxies (LBGs), Ly{alpha} emitters (LAEs) and extended Ly{alpha}-emitting blobs (LABs). The survey reaches ultimate (3 count) sensitivity limits of ~5.7x10^-17^ and ~3.0x10^-16^erg/cm^2^/s for the 0.5-2 and 2-8keV bands, respectively (corresponding to L_2-10keV_~5.7x10^42^erg/s and L_10-30keV_~2.0x10^43^erg/s at z=3.09, respectively, for an assumed photon index of {GAMMA}=1.4). These limits make SSA22 the fourth deepest extragalactic Chandra survey yet conducted, and the only one focused on a known high-redshift structure. In total, we detect 297 X-ray point sources and identify one obvious bright extended X-ray source over a ~330arcmin^2^ region. In addition to our X-ray catalogues, we provide all available optical spectroscopic redshifts and near-infrared and mid-infrared photometry available for our sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/554/742
- Title:
- Chandra Deep Survey of the HDF-N
- Short Name:
- J/ApJ/554/742
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A deep X-ray survey of the Hubble Deep Field-North (HDF-N) and its environs is performed using data collected by the Advanced CCD Imaging Spectrometer (ACIS) on board the Chandra X-Ray Observatory. Currently a 221.9ks exposure is available, the deepest ever presented, and here we give results on X-ray sources located in the 8.6'x8.7' area covered by the Caltech Faint Field Galaxy Redshift Survey (the "Caltech area"). This area has (1) deep photometric coverage in several optical and near-infrared bands; (2) extensive coverage at radio, submillimeter, and mid-infrared wavelengths; and (3) some of the deepest and most complete spectroscopic coverage ever obtained. It is also where the X-ray data have the greatest sensitivity; the minimum detectable fluxes in the 0.5-2keV (soft) and 2-8keV (hard) bands are ~1.3x10^-16^ and ~6.5x10^-16^ergs/cm^2^/s, respectively.
- ID:
- ivo://CDS.VizieR/J/ApJ/877/5
- Title:
- Chandra DF obscured & Compton-thick AGNs. I. Variability
- Short Name:
- J/ApJ/877/5
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a detailed X-ray spectral analysis of 1152 active galactic nuclei (AGNs) selected in the Chandra Deep Fields (CDFs), in order to identify highly obscured AGNs (N_H_>10^23^cm^-2^). By fitting spectra with physical models, 436 (38%) sources with L_X_>10^42^erg/s are confirmed to be highly obscured, including 102 Compton-thick (CT) candidates. We propose a new hardness ratio measure of the obscuration level that can be used to select highly obscured AGN candidates. The completeness and accuracy of applying this method to our AGNs are 88% and 80%, respectively. The observed log N-log S relation favors cosmic X-ray background models that predict moderate (i.e., between optimistic and pessimistic) CT number counts. Nineteen percent (6/31) of our highly obscured AGNs that have optical classifications are labeled as broad-line AGNs, suggesting that, at least for part of the AGN population, the heavy X-ray obscuration is largely a line-of-sight effect, i.e., some high column density clouds on various scales (but not necessarily a dust-enshrouded torus) along our sight line may obscure the compact X-ray emitter. After correcting for several observational biases, we obtain the intrinsic N_H_ distribution and its evolution. The CT/highly obscured fraction is roughly 52% and is consistent with no evident redshift evolution. We also perform long-term (~17yr in the observed frame) variability analyses for 31 sources with the largest number of counts available. Among them, 17 sources show flux variabilities: 31% (5/17) are caused by the change of N_H_, 53% (9/17) are caused by the intrinsic luminosity variability, 6% (1/17) are driven by both effects, and 2 are not classified owing to large spectral fitting errors.
- ID:
- ivo://CDS.VizieR/J/MNRAS/355/97
- Title:
- Chandra/ELAIS mid-infrared sources
- Short Name:
- J/MNRAS/355/97
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a cross-correlation of the European Large Area Infrared Space Observatory (ISO) survey (ELAIS) with the ELAIS Deep X-ray Survey of the N1 and N2 fields. There are seven Chandra point sources with matches in the ELAIS Final Analysis 15{mu}m catalogue, out of a total of 28 extragalactic ISO sources present in the Chandra fields. Five of these are consistent with active galactic nuclei (AGN) giving an AGN fraction of ~19 per cent in the 15{mu}m flux range 0.8-6mJy. We have co-added the hard X-ray fluxes of the individually undetected ISO sources and find a low significance detection consistent with star formation in the remaining population. We combine our point source cross-correlation fraction with the XMM-Newton observations of the Lockman Hole and Chandra observations of the Hubble Deep Field North to constrain source count models of the mid-infrared galaxy population. The low dust-enshrouded AGN fraction in ELAIS implied by the number of cross-identifications between the ELAIS mid-infrared sample and the Chandra point sources is encouraging for the use of mid-infrared surveys to constrain the cosmic star formation history, provided there are not further large undetected populations of Compton-thick AGN.