- ID:
- ivo://CDS.VizieR/J/ApJ/645/955
- Title:
- ChaMP serendipitous galaxy cluster survey
- Short Name:
- J/ApJ/645/955
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a survey of serendipitous extended X-ray sources and optical cluster candidates from the Chandra Multiwavelength Project (ChaMP). Our main goal is to make an unbiased comparison of X-ray and optical cluster detection methods. In 130 archival Chandra pointings covering 13deg^2^, we use a wavelet decomposition technique to detect 55 extended sources, of which 6 are nearby single galaxies. Our X-ray cluster catalog reaches a typical flux limit of about 10^-14^ergs/cm^2^/s, with a median cluster core radius of 21". For 56 of the 130 X-ray fields, we use the ChaMP's deep NOAO 4m MOSAIC g', r', and i' imaging to independently detect cluster candidates using a Voronoi tessellation and percolation (VTP) method. Red-sequence filtering decreases the galaxy fore- and background contamination and provides photometric redshifts to z~0.7. From the overlapping 6.1deg^2^ X-ray/optical imaging, we find 115 optical clusters (of which 11% are in the X-ray catalog) and 28 X-ray clusters (of which 46% are in the optical VTP catalog).
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/728/27
- Title:
- Chandra and AAOmega observations of Abell 2744
- Short Name:
- J/ApJ/728/27
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- New Chandra X-ray data and extensive optical spectroscopy, obtained with AAOmega on the 3.9m Anglo-Australian Telescope, are used to study the complex merger taking place in the galaxy cluster Abell 2744. Combining our spectra with data from the literature provides a catalog of 1237 redshifts for extragalactic objects lying within 15' of the cluster center. From these, we confirm 343 cluster members projected within 3Mpc of the cluster center. Combining positions and velocities, we identify two major substructures, corresponding to the remnants of two major subclusters. The new data are consistent with a post-core-passage, major merger taking place along an axis that is tilted well out of the plane of the sky, together with an interloping minor merger. Supporting this interpretation, the new X-ray data reveal enriched, low entropy gas from the core of the approaching, major subcluster, lying ~2' north of the cluster center, and a shock front to the southeast of the previously known bright, compact core associated with the receding subcluster. The X-ray morphology of the compact core is consistent with a Bullet-like cluster viewed from within ~45{deg} of the merger axis. An X-ray peak ~3' northwest of the cluster center, with an associated cold front to the northeast and a trail of low entropy gas to the south, is interpreted as the remnant of an interloping minor merger taking place roughly in the plane of the sky. We infer approximate paths for the three merging components.
- 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/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/ApJS/197/24
- Title:
- Chandra large-scale extragalactic jets. I.
- Short Name:
- J/ApJS/197/24
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we report the first stages of an investigation into the X-ray properties of extragalactic jets (XJET project). Our approach is to subject all sources for which X-ray emission has been detected by Chandra to uniform reduction procedures. Using Chandra archival data for 106 such sources, we measure X-ray fluxes in three bands and compare these to radio fluxes. We discuss the sample, the reduction methods, and present first results for the ratio of X-ray to radio flux for jet knots and hotspots. In particular, we apply statistical tests to various distributions of key observational parameters to evaluate differences between the different classes of sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/690/295
- Title:
- Chandra observations of J1604+4314 supercluster
- Short Name:
- J/ApJ/690/295
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of Chandra observations of the Cl1604 supercluster at z~0.9. The system is the largest structure mapped at redshifts approaching unity, containing at least eight spectroscopically confirmed galaxy clusters and groups. Using two 50ks ACIS-I pointings we examine both the X-ray point-source population and the diffuse emission from individual clusters in the system. Over an area encompassing the entire supercluster (~0.154deg^2^), we find a 2.5{sigma} excess of point sources detected in the hard band (2-10keV) relative to the number of sources found in blank fields observed by Chandra. No such excess is observed in the soft band (0.5-2keV). The hard-band source density is 1.47 times greater than that of a blank field, in agreement with the previously reported correlation between overdensity amplitude and cluster redshift. Using a maximum likelihood technique, we have matched 112 of the 161 detected X-ray point sources to optical counterparts and found 15 sources that are associated with the supercluster. All 15 sources have rest-frame luminosities consistent with emission from active galactic nuclei (AGNs).
- ID:
- ivo://CDS.VizieR/J/ApJ/681/1017
- Title:
- Chandra observations of lens groups
- Short Name:
- J/ApJ/681/1017
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a systematic investigation of the X-ray properties of a sample of moderate-redshift (0.3<z<0.6) galaxy groups. These groups were selected not by traditional X-ray or optical search methods, but rather by an association, either physical or along the line of sight, with a strong gravitational lens. We calculate the properties of seven galaxy groups in the fields of six lens systems. Diffuse X-ray emission from the intragroup medium is detected in four of the groups. All of the detected groups have X-ray luminosities greater than 10^42^h^-2^ergs/s and lie on the L_X_^-{sigma}_v_^ relations defined by local groups and clusters. The upper limits for the nondetections are also consistent with the local L_X_^-{sigma}_v_^ relationships. Although the sample size is small and deeper optical and X-ray data are needed, these results suggest that lens-selected groups are similar to X-ray-selected samples and thus are more massive than the typical poor-group environments of local galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/900/79
- Title:
- Chandra obs. of SDSS AGN pairs at z_med_~0.1
- Short Name:
- J/ApJ/900/79
- Date:
- 21 Mar 2022 09:29:38
- Publisher:
- CDS
- Description:
- We present a Chandra archival study of optically selected active galactic nucleus (AGN) pairs at a median redshift z~0.1. Out of 1286 AGN pairs (with projected separations rp<100kpc and velocity offsets {Delta}v<600km/s) optically identified from the Sloan Digital Sky Survey Seventh Data Release, we find 67 systems with archival Chandra observations, which represents the largest sample of optically selected AGN pairs studied in the X-ray. Among the 67 AGN pairs, 21 systems have both nuclei detected in the X-ray, 36 have one nucleus detected in the X-ray, and 10 have no X-ray detection. The X-ray detection rate, 78/134=58% (+/-7% 1{sigma} Poisson errors), is significantly higher than that (23/134=17%+/-4%) of a comparison sample of star-forming galaxy pairs, lending support to the optical AGN classification. In the conservative case where X-ray contamination from star formation is removed, the X-ray detection rate becomes 27%+/-4%, consistent with predictions from the latest galaxy merger simulations. The 2-10keV X-ray luminosity L2-10keV increases with decreasing projected separation in AGN pairs for rp>~15kpc, suggesting an enhancement of black hole accretion even in early-stage mergers. On the other hand, L2-10keV appears to decrease with decreasing projected separation at rp<~15kpc, which is contradictory to predictions from merger simulations. The apparent decrease in L2-10 keV of AGN pairs at rp<~15kpc may be caused by (i) enhanced absorbing columns from merger-induced gas inflows, (ii) feedback effects from early-stage mergers, and/or (iii) small number statistics. Future X-ray studies with larger samples are needed to put our results on firmer statistical ground.
- ID:
- ivo://CDS.VizieR/J/ApJS/168/19
- Title:
- Chandra sources in 5 galaxy clusters
- Short Name:
- J/ApJS/168/19
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present catalogs and images of optical counterparts to the Chandra-selected X-ray sources found in the fields of the five clusters RX J0152-1357, RX J0849+4452, RDCS J0910+5422, MS 1054-0321, and RDCS J1252-2927, which were imaged with the Advanced Camera for Surveys as part of the ACS Guaranteed Time Observer programs. A total of 98 X-ray sources fall within the ACS mosaics, and positive identifications are made for ~96% of them, including confirmed cluster members. We classify the sources as active galactic nuclei (AGNs) or QSOs depending on their X-ray output.