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1941. The Chandra Deep Fields North and South
ID:
ivo://CDS.VizieR/J/AJ/126/539
Title:
The Chandra Deep Fields North and South
Short Name:
J/AJ/126/539
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present point-source catalogs for the ~2Ms exposure of the Chandra Deep Field North, currently the deepest X-ray observation of the universe in the 0.5-8.0keV band. Five hundred and three (503) X-ray sources are detected over an ~448arcmin^2^ area in up to seven X-ray bands. Twenty (20) of these X-ray sources lie in the central 5.3 arcmin^2^ Hubble Deep Field North (13600^+3800^_-3000_sources/deg^2^). The on-axis sensitivity limits are 2.5x10^-17^ergs/cm^2^/s (0.5-2.0keV) and 1.4x10^-16^ergs/cm^2^/s (2-8keV). Source positions are determined using matched-filter and centroiding techniques; the median positional uncertainty is ~0.3". To allow consistent comparisons, the point-source catalogs for the 1Ms Chandra Deep Field South (CDF-S; see Cat. J/ApJS/139/369) have also been produced. Three hundred and twenty-six (326) X-ray sources are included in the main Chandra South 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.
1942. The Chandra Source Catalog (CSC), Release 2.0
ID:
ivo://CDS.VizieR/IX/57
Title:
The Chandra Source Catalog (CSC), Release 2.0
Short Name:
IX/57
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Chandra Source Catalog (CSC) is the definitive catalog of X-ray sources detected by the Chandra X-ray Observatory. By combining Chandra's sub-arcsecond on-axis spatial resolution and low instrumental background with consistent data processing, the CSC delivers a wide variety of uniformly calibrated properties and science ready data products for detected sources over four decades of flux. The second major release of the catalog, CSC 2.0, includes measured properties for 317,167 unique compact and extended X-ray sources in the sky, allowing statistical analysis of large samples, as well as individual source studies. The sensitivity limit for compact sources in CSC 2.0 is ~5 net counts (a factor of >~2 better than the previous catalog release). This improvement is achieved by using a two-stage approach that involves co-adding multiple observations of the same field prior to source detection, and then using an optimized source detection method.
1943. The Chandra Source Catalog, Release 1.1
ID:
ivo://CDS.VizieR/IX/45
Title:
The Chandra Source Catalog, Release 1.1
Short Name:
IX/45
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Chandra Source Catalog (CSC) is a general purpose virtual X-ray astrophysics facility that provides access to a carefully selected set of generally useful quantities for individual X-ray sources, and is designed to satisfy the needs of a broad-based group of scientists, including those who may be less familiar with astronomical data analysis in the X-ray regime. The first release of the CSC includes information about 94,676 distinct X-ray sources detected in a subset of public Advanced CCD Imaging Spectrometer imaging observations from roughly the first eight years of the Chandra mission. This release of the catalog includes point and compact sources with observed spatial extents <~30''. The catalog (1) provides access to the best estimates of the X-ray source properties for detected sources, with good scientific fidelity, and directly supports scientific analysis using the individual source data; (2) facilitates analysis of a wide range of statistical properties for classes of X-ray sources; and (3) provides efficient access to calibrated observational data and ancillary data products for individual X-ray sources, so that users can perform detailed further analysis using existing tools. The catalog includes real X-ray sources detected with flux estimates that are at least 3 times their estimated 1-{sigma} uncertainties in at least one energy band, while maintaining the number of spurious sources at a level of <~1 false source per field for a 100ks observation. For each detected source, the CSC provides commonly tabulated quantities, including source position, extent, multi-band fluxes, hardness ratios, and variability statistics, derived from the observations in which the source is detected. In addition to these traditional catalog elements, for each X-ray source the CSC includes an extensive set of file-based data products that can be manipulated interactively, including source images, event lists, light curves, and spectra from each observation in which a source is detected.
1944. The Chandra UDS survey (X-UDS)
ID:
ivo://CDS.VizieR/J/ApJS/236/48
Title:
The Chandra UDS survey (X-UDS)
Short Name:
J/ApJS/236/48
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the X-UDS survey, a set of wide and deep Chandra observations of the Subaru-XMM Deep/UKIDSS Ultra Deep Survey (SXDS/UDS) field. The survey consists of 25 observations that cover a total area of 0.33deg^2^. The observations are combined to provide a nominal depth of ~600ks in the central 100arcmin^2^ region of the field that has been imaged with Hubble/WFC3 by the CANDELS survey and ~200ks in the remainder of the field. In this paper, we outline the survey's scientific goals, describe our observing strategy, and detail our data reduction and point source detection algorithms. Our analysis has resulted in a total of 868 band-merged point sources detected with a false-positive Poisson probability of <1x10^-4^. In addition, we present the results of an X-ray spectral analysis and provide best-fitting neutral hydrogen column densities, N_H_, as well as a sample of 51 Compton-thick active galactic nucleus candidates. Using this sample, we find the intrinsic Compton-thick fraction to be 30%-35% over a wide range in redshift (z=0.1-3), suggesting the obscured fraction does not evolve very strongly with epoch. However, if we assume that the Compton-thick fraction is dependent on luminosity, as is seen for Compton-thin sources, then our results are consistent with a rise in the obscured fraction out to z~3. Finally, an examination of the host morphologies of our Compton-thick candidates shows a high fraction of morphological disturbances, in agreement with our previous results.
1945. The CIDA Variability Survey of Orion OB1. II.
ID:
ivo://CDS.VizieR/J/AJ/157/85
Title:
The CIDA Variability Survey of Orion OB1. II.
Short Name:
J/AJ/157/85
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of our large-scale, optical, multi-epoch photometric survey across ~180 square degrees in the Orion OB1 association, complemented with extensive follow-up spectroscopy. Our focus is mapping and characterizing the off-cloud, low-mass, pre-main-sequence (PMS) populations. We report 2062 K- and M-type confirmed T Tauri members; 59% are located in the OB1a subassociation, 27% in the OB1b subassociation, and the remaining 14% in the A and B molecular clouds. We characterize two new clusterings of T Tauri stars, the HD 35762 and HR 1833 groups, both located in OB1a not far from the 25 Ori cluster. We also identify two stellar overdensities in OB1b, containing 231 PMS stars, and find that the OB1b region is composed of two populations at different distances, possibly due to the OB1a subassociation overlapping with the front of OB1b. A ~2 deg wide halo of young stars surrounds the Orion Nebula Cluster, corresponding in part to the low-mass populations of NGC 1977 and NGC 1980. We use the strength of H{alpha} in emission, combined with the IR excess and optical variability, to define a new type of T Tauri star, the C/W class, stars we propose may be nearing the end of their accretion phase, in an evolutionary state between classical and weak-lined T Tauri stars. The evolution of the ensemble-wide equivalent width of Li I{lambda}6707 indicates a Li depletion timescale of ~8.5 Myr. Disk accretion declines with an e-folding timescale of ~2 Myr, consistent with previous studies.
1946. The Clowes-Campusano LQG Survey. I.
ID:
ivo://CDS.VizieR/J/ApJ/702/506
Title:
The Clowes-Campusano LQG Survey. I.
Short Name:
J/ApJ/702/506
Date:
21 Oct 2021
Publisher:
CDS
Description:
The nature of galaxy structures on large scales is a key observational prediction for current models of galaxy formation. The Sloan Digital Sky Survey (SDSS) and the 2dF galaxy survey have revealed a number of structures on 40-150h<SUP>&#8211;1</SUP>Mpc scales at low redshifts, and some even larger ones. To constrain galaxy number densities, luminosities, and stellar populations in large structures at higher redshift, we have investigated two sheet-like structures of galaxies at z=0.8 and 1.3 spanning 150h<SUP>&#8211;1</SUP> comoving Mpc embedded in large quasar groups (LQGs) extending over at least 200h<SUP>&#8211;1</SUP>Mpc. We present first results of an analysis of these sheet-like structures using two contiguous 1&#176; Galaxy Evolution Explorer (GALEX) fields (FUV and NUV) cross-correlated with optical data from the SDSS. We derive a sample of 462 Lyman break galaxy (LBG) candidates coincident with the sheets. Using the GALEX and SDSS data, we show that the overall average spectral energy distribution of a LBG galaxy at z&#8764;1 is flat (in f<SUB>&#955;</SUB>) in the rest-frame wavelength range from 1500&Aring; to 4000&Aring;, implying evolved populations of stars in the LBGs. From the luminosity functions we get indications for overdensities in the two LQGs compared to their foreground regions.
1947. The CMT CCD Drift Scan Survey
ID:
ivo://CDS.VizieR/I/282
Title:
The CMT CCD Drift Scan Survey
Short Name:
I/282
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is CMC12 (Version 1.0), an astrometric and photometric catalogue of 6.3 million stars in the red magnitude range 9 to 17. The Carlsberg Meridian Telescope (CMT) underwent a major upgrade in March 1999. A 2k by 2k CCD camera was installed with a Sloan r' filter operating in a drift scan mode. With the new system, the magnitude limit is r'_CMT_=17 and the positional accuracy is about 0.035". The main task of the CMT is to map the sky in the declination range -3{deg} to +30{deg} with the aim of providing an astrometric, and photometric, catalogue that can accurately transfer the Hipparcos/Tycho reference frame to Schmidt plates. The current release (Version 1.0) comprises all the observations made between March 1999 and March 2002 with the new CCD in the declination band -3{deg} to +3{deg}. It is intended to release the rest of the catalogue later. A more complete description is available in the documentation at http://www.ast.cam.ac.uk/~dwe/SRF/cmc12/cmc12_documentation.ps or http://www.ast.cam.ac.uk/~dwe/SRF/cmc12/cmc12_documentation.pdf
1948. The CNOC2 survey. I.
ID:
ivo://CDS.VizieR/J/ApJS/129/475
Title:
The CNOC2 survey. I.
Short Name:
J/ApJS/129/475
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Canadian Network for Observational Cosmology Field Galaxy Redshift Survey (CNOC2) obtained spectroscopic redshifts for about 6200 galaxies to a nominal limit of R=21.5. The survey area of about 1.5 square degrees was spread over four patches on the sky. This catalog presents photometry and redshifts for all galaxies in the CNOC2 0223+00 Patch (area of 1409 square arcminutes). A future paper will provide catalogs for the other three patches.
1949. The COSMOS-Legacy Survey (CLS) catalog
ID:
ivo://CDS.VizieR/J/ApJ/819/62
Title:
The COSMOS-Legacy Survey (CLS) catalog
Short Name:
J/ApJ/819/62
Date:
21 Oct 2021
Publisher:
CDS
Description:
The COSMOS-Legacy survey is a 4.6Ms Chandra program that has imaged 2.2deg^2^ of the COSMOS field with an effective exposure of ~160ks over the central 1.5deg^2^ and of ~80ks in the remaining area. The survey is the combination of 56 new observations obtained as an X-ray Visionary Project with the previous C-COSMOS survey. We describe the reduction and analysis of the new observations and the properties of 2273 point sources detected above a spurious probability of 2x10^-5^. We also present the updated properties of the C-COSMOS sources detected in the new data. The whole survey includes 4016 point sources (3814, 2920 and 2440 in the full, soft, and hard band). The limiting depths are 2.2x10^-16^, 1.5x10^-15^, and 8.9x10^-16^erg/cm^2^/s in the 0.5-2, 2-10, and 0.5-10keV bands, respectively. The observed fraction of obscured active galactic nuclei with a column density >10^22^/cm^2^ from the hardness ratio (HR) is ~50^+17^_-16_%. Given the large sample we compute source number counts in the hard and soft bands, significantly reducing the uncertainties of 5%-10%. For the first time we compute number counts for obscured (HR>-0.2) and unobscured (HR<-0.2) sources and find significant differences between the two populations in the soft band. Due to the unprecedent large exposure, COSMOS-Legacy area is three times larger than surveys at similar depths and its depth is three times fainter than surveys covering similar areas. The area-flux region occupied by COSMOS-Legacy is likely to remain unsurpassed for years to come.
1950. The C3R2 survey: DR2 new spectroscopic redshifts
ID:
ivo://CDS.VizieR/J/ApJ/877/81
Title:
The C3R2 survey: DR2 new spectroscopic redshifts
Short Name:
J/ApJ/877/81
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Complete Calibration of the Color-Redshift Relation (C3R2) survey is a multi-institution, multi-instrument survey that aims to map the empirical relation of galaxy color to redshift to i~24.5 (AB), thereby providing a firm foundation for weak lensing cosmology with the Stage IV dark energy missions Euclid and WFIRST. Here we present 3171 new spectroscopic redshifts obtained in the 2016B and 2017A semesters with a combination of DEIMOS, LRIS, and MOSFIRE on the Keck telescopes. The observations come from all of the Keck partners: Caltech, NASA, the University of Hawaii, and the University of California. Combined with the 1283 redshifts published in DR1, the C3R2 survey has now obtained and published 4454 high-quality galaxy redshifts. We discuss updates to the survey design and provide a catalog of photometric and spectroscopic data. Initial tests of the calibration method performance are given, indicating that the sample, once completed and combined with extensive data collected by other spectroscopic surveys, should allow us to meet the cosmology requirements for Euclid, and make significant headway toward solving the problem for WFIRST. We use the full spectroscopic sample to demonstrate that galaxy brightness is weakly correlated with redshift once a galaxy is localized in the Euclid or WFIRST color space, with potentially important implications for the spectroscopy needed to calibrate redshifts for faint WFIRST and LSST sources.

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