- ID:
- ivo://CDS.VizieR/J/ApJ/588/1009
- Title:
- Chandra X-ray observations of NGC 2516
- Short Name:
- J/ApJ/588/1009
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a comprehensive study of the Chandra X-ray observations of the young open cluster NGC 2516. We have analyzed eight individual Chandra observations. We have combined the data to achieve the greatest sensitivity, reaching down to log f_X_=-14.56(erg/s/cm^2^), or logLX=28.69(erg/s) at the distance of NGC 2516. Out of 284 X-ray sources detected, 155 are identified with photometric cluster members, with very little ambiguity.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJ/586/826
- Title:
- Chandra X-ray observations of NGC 1316
- Short Name:
- J/ApJ/586/826
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We report the results of the Chandra ACIS subarcsecond resolution X-ray observation of the archetypal merger radio galaxy NGC 1316 (Fornax A).
- ID:
- ivo://CDS.VizieR/J/ApJ/598/375
- Title:
- Chandra X-ray observations of NGC 2024
- Short Name:
- J/ApJ/598/375
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results of a sensitive 76ks Chandra observation of the young stellar cluster in NGC 2024, lying at a distance of ~415pc in the Orion B giant molecular cloud. Previous infrared observations have shown that this remarkable cluster contains several hundred embedded young stars, most of which are still surrounded by circumstellar disks. Thus, it presents a rare opportunity to study X-ray activity in a large sample of optically invisible protostars and classical T Tauri stars (CTTSs) undergoing accretion. Chandra detected 283 X-ray sources, of which 248 were identified with counterparts at other wavelengths, mostly in the near-infrared. Astrometric registration of Chandra images against the Two Micron All Sky Survey (2MASS) resulted in positional offsets of ~0.25" near field center, yielding high confidence identifications of infrared counterparts.
- ID:
- ivo://CDS.VizieR/J/ApJ/746/54
- Title:
- Chandra X-ray observations of SDSS-DR5 QSOs
- Short Name:
- J/ApJ/746/54
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We analyze the X-ray variability of 264 Sloan Digital Sky Survey spectroscopic quasars using the Chandra public archive. This data set consists of quasars with spectroscopic redshifts out to z {approx} 5 and covers rest-frame timescales up to {Delta}t_sys_{approx} 2000 days, with three or more X-ray observations available for 82 quasars. It therefore samples longer timescales and higher luminosities than previous large-scale analyses of active galactic nucleus (AGN) variability. We find significant ( >~ 3{sigma}) variation in {approx}30% of the quasars overall; the fraction of sources with detected variability increases strongly with the number of available source counts up to {approx}70% for sources with >= 1000 counts per epoch. Assuming that the distribution of fractional variation is Gaussian, its standard deviation is {approx}16% on >~ 1 week timescales, which is not enough to explain the observed scatter in quasar X-ray-to-optical flux ratios as being due to variability alone. We find no evidence in our sample that quasars are more variable at higher redshifts (z > 2), as has been suggested in previous studies. Quasar X-ray spectra vary similarly to some local Seyfert AGNs in that they steepen as they brighten, with evidence for a constant, hard spectral component that is more prominent in fainter stages. We identify one highly variable Narrow Line Seyfert 1-type spectroscopic quasar in the Chandra Deep Field-North. We constrain the rate of kilosecond-timescale flares in the quasar population using {approx}8 months of total exposure and also constrain the distribution of variation amplitudes between exposures; extreme changes (>100%) are quite rare, while variation at the 25% level occurs in <25% of observations. [O III] {lambda}5007 {AA} emission may be stronger in sources with lower levels of X-ray variability; if confirmed, this would represent an additional link between small-scale (corona) and large-scale (narrow-line region) AGN properties.
- ID:
- ivo://CDS.VizieR/J/ApJS/238/23
- Title:
- Chandra X-ray point sources in Abell 133
- Short Name:
- J/ApJS/238/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- As an evolutionary phase of galaxies, active galactic nuclei (AGNs) over a large range of redshifts have been utilized for understanding cosmic evolution. In particular, the population and evolution of AGNs have been investigated through the study of the cosmic X-ray background in various fields. As one of the deep fields observed by Chandra, with a total of 2.8Ms exposures, Abell 133 is a special region for investigating AGNs, providing a testbed for probing the environmental effects on AGN triggers, since cluster environments can be different from field environments. The achieved flux limits of data at the 50% completeness levels of 6.95x10^-16^, 1.43x10^-16^, and 1.57x10^-15^erg/s/cm^2^ are 0.5-8, 0.5-2, and 2-8keV. Using the wavdetect and no-source binomial probability (i.e., p<0.007), we analyze the combined Chandra image, detecting 1617 (in 0.5-8keV), 1324 (in 0.5-2keV), and 1028 (in 2-8keV) X-ray point sources in the Abell 133 region. Here, we present the X-ray point source catalog with the source fluxes, which can be combined with multiwavelength data for future works. We find that the number count distribution of the X-ray point sources is well reproduced with a broken power-law model, while the best-fit model parameters are sensitive to the fitting range of the number count distribution. Finally, we find an excess of number density (a decrease of AGN fraction) at the central region of the cluster, which reflects the effect of dense environments on AGN triggers, a finding similar to those of other studies of galaxy clusters.
- ID:
- ivo://CDS.VizieR/J/ApJ/560/675
- Title:
- Chandra X-ray point sources in Cen A
- Short Name:
- J/ApJ/560/675
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from two Chandra X-ray Observatory observations of the X-ray point source population in the nearby radio galaxy Centaurus A (NGC 5128). Using a wavelet decomposition detection algorithm, we detect 246 individual point sources above a limiting luminosity of ~2*10^36^ergs/s, 82 of which are detected in both data sets where the fields of view overlap. Thirty-eight sources were detected in only one observation but were within the field of view of both pointings, implying considerable variability. We identify eight foreground stars in our observations. We also identify nine of the sources with known globular clusters in Centaurus A. All previously observed ROSAT sources within our field of view are detected.
- ID:
- ivo://CDS.VizieR/J/A+A/447/71
- Title:
- CHANDRA X-ray point sources in Cen A (NGC 5128)
- Short Name:
- J/A+A/447/71
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have studied the X-ray point source population of Centaurus A (NGC 5128) using data from four archival CHANDRA observations. We detected 272 point-like X-ray sources within a radius of 10' from the centre. Approximately half of these are CXB sources, with the remaining half being LMXBs. The spatial distribution of the LMXBs, both azimuthally averaged and 2D, is consistent with the distribution of the K-band light observed in the 2MASS survey. After correction for the incompleteness effect we constrain the LMXB luminosity function down to ~2x10^36^erg/s, much lower than previous studies of LMXBs in elliptical galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/602/231
- Title:
- Chandra X-ray point sources in nearby galaxies
- Short Name:
- J/ApJ/602/231
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have analyzed Chandra ACIS observations of 32 nearby spiral and elliptical galaxies and present the results of 1441 X-ray point sources that were detected in these galaxies. The total point-source X-ray (0.3-8.0keV) luminosity L_XP_ is well correlated with the B-band, K-band, and FIR+UV luminosities of spiral host galaxies and is well correlated with the B-band and K-band luminosities of elliptical galaxies. This suggests an intimate connection between L_XP_ and both the old and young stellar populations, for which K and FIR+UV luminosities are reasonable proxies for the galaxy mass M and star formation rate SFR.
- ID:
- ivo://CDS.VizieR/J/ApJ/876/53
- Title:
- Chandra X-ray point sources in the Fornax cluster
- Short Name:
- J/ApJ/876/53
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Based on archival Chandra observations with a total exposure of 1.3Ms, we study X-ray point sources in the Fornax cluster of galaxies, with the primary aim of searching for intracluster X-ray source populations. We detect 1177 point sources out to a projected radius of ~30' (~180kpc) from the cluster center and down to a limiting 0.5-8keV luminosity of ~3x10^37^erg/s. We construct the source surface density profile, after excluding sources associated with foreground stars, known globular clusters, ultra-compact dwarfs, and galactic nuclei. From this profile we statistically identify ~183 excess sources that are not associated with the bulk stellar content of the individual member galaxies of Fornax, nor with the cosmic X-ray background. Taking into account Poisson error and cosmic variance, the cumulative significance of this excess is at the >~2{sigma} level (with a maximum of 3.6{sigma}) outside three effective radii of the central giant elliptical, NGC 1399. The luminosity function of the excess sources is found to be significantly steeper than that of the GC-hosting sources (presumably low-mass X-ray binaries (LMXBs)), disfavoring the possibility that unidentified GCs are primarily responsible for the excess. We show that a large fraction of the excess can be related to the extended stellar halo of NGC 1399 and/or the diffuse intracluster light, thus providing strong evidence for the presence of intracluster X-ray sources in Fornax, the second unambiguous case for a galaxy cluster after Virgo. Other possible origins of the excess, including supernova-kicked LMXBs and stripped nucleated dwarf galaxies are discussed.
- ID:
- ivo://CDS.VizieR/J/ApJ/758/15
- Title:
- Chandra X-ray point sources of NGC 300
- Short Name:
- J/ApJ/758/15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the source catalog of a new Chandra ACIS-I observation of NGC 300 obtained as part of the Chandra Local Volume Survey. Our 63ks exposure covers ~88% of the D_25_ isophote (R{approx}6.3kpc) and yields a catalog of 95 X-ray point sources detected at high significance to a limiting unabsorbed 0.35-8 keV luminosity of ~10^36^erg/s. Sources were cross-correlated with a previous XMM-Newton catalog, and we find 75 "X-ray transient candidate" sources that were detected by one observatory, but not the other. We derive an X-ray scale length of 1.7+/-0.2kpc and a recent star formation rate of 0.12M_{sun}_/yr in excellent agreement with optical observations. Deep, multi-color imaging from the Hubble Space Telescope, covering ~32% of our Chandra field, was used to search for optical counterparts to the X-ray sources, and we have developed a new source classification scheme to determine which sources are likely X-ray binaries, supernova remnants, and background active galactic nucleus candidates. Finally, we present the X-ray luminosity functions (XLFs) at different X-ray energies, and we find the total NGC 300 X-ray point-source population to be consistent with other late-type galaxies hosting young stellar populations (<~50Myr). We find that XLF of sources associated with older stellar populations has a steeper slope than the XLF of X-ray sources coinciding with young stellar populations, consistent with theoretical predictions.
