- ID:
- ivo://CDS.VizieR/J/ApJ/695/1094
- Title:
- Chandra observations of NGC 4636
- Short Name:
- J/ApJ/695/1094
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the X-ray point-source population in the nearby Virgo elliptical galaxy NGC 4636 from three Chandra X-ray observations. These observations, totaling ~193ks after time filtering, were taken with the Advanced CCD Imaging Camera (ACIS) over a three-year period. Using a wavelet decomposition detection algorithm, we detect 318 individual point sources. For our analysis, we use a subset of 277 detections with >=net 10 counts (a limiting luminosity of approximately 1.2x10^37^erg/s in the 0.5-2keV band, outside the central 1.5' bright galaxy core). We present a radial distribution of the point sources. Between 1.5' and 6' from the center, 25% of our sources are likely to be background sources (active galactic nuclei (AGNs)) and 75% are low-mass X-ray binaries (LMXBs) within the galaxy, while at radial distances greater than 6', background sources (AGN) will dominate the point sources. We find 77 matches between X-ray point sources and globular cluster (GC) candidates found in deep optical images of NGC 4636. In the annulus from 1.5' to 6' of the galaxy center, 48 of the 129 X-ray point sources (37%) with >=10 net counts are matched with GC candidates. Since we expect 25% of these sources to be background AGN, the percentage matched with GCs could be as high as 50%. Of these matched sources, we find that ~70% are associated with the redder GC candidates, those that are thought to have near-solar metal abundance.
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- ID:
- ivo://CDS.VizieR/J/ApJ/758/105
- Title:
- Chandra observations of NGC2903 central regions
- Short Name:
- J/ApJ/758/105
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a deep Chandra observation of the central regions of the late-type barred spiral galaxy NGC 2903. The Chandra data reveal soft (kT_e_~0.2-0.5keV) diffuse emission in the nuclear starburst region and extending ~2' (~5kpc) to the north and west of the nucleus. Much of this soft hot gas is likely to be from local active star-forming regions; however, besides the nuclear region, the morphology of hot gas does not strongly correlate with the bar or other known sites of active star formation. The central ~650pc radius starburst zone exhibits much higher surface brightness diffuse emission than the surrounding regions and a harder spectral component in addition to a soft component similar to the surrounding zones. We interpret the hard component as also being of thermal origin with kT_e_~3.6keV and to be directly associated with a wind fluid produced by supernovae and massive star winds similar to the hard diffuse emission seen in the starburst galaxy M82. The inferred terminal velocity for this hard component, ~1100km/s, exceeds the local galaxy escape velocity suggesting a potential outflow into the halo and possibly escape from the galaxy gravitational potential. Morphologically, the softer extended emission from nearby regions does not display an obvious outflow geometry. However, the column density through which the X-rays are transmitted is lower in the zone to the west of the nucleus compared to that from the east and the surface brightness is relatively higher suggesting some of the soft hot gas originates from above the disk: viewed directly from the western zone but through the intervening disk of the host galaxy along sight lines from the eastern zone. There are several point-like sources embedded in the strong diffuse nuclear emission zone. Their X-ray spectra show them to likely be compact binaries. None of these detected point sources are coincident with the mass center of the galaxy and we place an upper limit luminosity from any point-like nuclear source to be <2x10^38^erg/s in the 0.5-8.0keV band, which indicates that NGC 2903 lacks an active galactic nucleus. Heating from the nuclear starburst and a galactic wind may be responsible for preventing cold gas from accreting onto the galactic center.
- ID:
- ivo://CDS.VizieR/J/ApJS/243/3
- Title:
- Chandra observations of SINGS galaxies
- Short Name:
- J/ApJS/243/3
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present new Chandra constraints on the X-ray luminosity functions (XLFs) of X-ray binary (XRB) populations, as well as their scaling relations, for a sample of 38 nearby galaxies (D=3.4-29Mpc). Our galaxy sample is drawn primarily from the Spitzer Infrared Nearby Galaxies Survey (SINGS) and contains a wealth of Chandra (5.8Ms total) and multiwavelength data, allowing for star formation rates (SFRs) and stellar masses (M_*_) to be measured on subgalactic scales. We divided the 2478 X-ray-detected sources into 21 subsamples in bins of specific SFR (sSFR=SFR/M_*_) and constructed XLFs. To model the XLF dependence on sSFR, we fit a global XLF model, containing contributions from high-mass XRBs (HMXBs), low-mass XRBs (LMXBs), and background sources from the cosmic X-ray background that respectively scale with SFR, M_*_, and sky area. We find an HMXB XLF that is more complex in shape than previously reported and an LMXB XLF that likely varies with sSFR, potentially due to an age dependence. When applying our global model to XLF data for each individual galaxy, we discover a few galaxy XLFs that significantly deviate from our model beyond statistical scatter. Most notably, relatively low-metallicity galaxies have an excess of HMXBs above ~10^38^erg/s, and elliptical galaxies that have relatively rich populations of globular clusters (GCs) show excesses of LMXBs compared to the global model. Additional modeling of how the XRB XLF depends on stellar age, metallicity, and GC specific frequency is required to sufficiently characterize the XLFs of galaxies.
- ID:
- ivo://CDS.VizieR/J/ApJ/765/87
- Title:
- Chandra observations of the 2QZ Cluster 1004+00
- Short Name:
- J/ApJ/765/87
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a {approx}100ks Chandra observation of the 2QZ Cluster 1004+00 structure at z=2.23 (hereafter 2QZ Clus). 2QZ Clus was originally identified as an overdensity of four optically-selected QSOs at z=2.23 within a 15x15arcmin^2^ region. Narrow-band imaging in the near-IR (within the K band) revealed that the structure contains an additional overdensity of 22 z=2.23 H{alpha}-emitting galaxies (HAEs), resulting in 23 unique z=2.23 HAEs/QSOs (22 within the Chandra field of view). Our Chandra observations reveal that three HAEs in addition to the four QSOs harbor powerfully accreting supermassive black holes (SMBHs), with 2-10keV luminosities of ~(8-60)x10^43^erg/s and X-ray spectral slopes consistent with unobscured active galactic nucleus (AGN). Using a large comparison sample of 210 z=2.23 HAEs in the Chandra-COSMOS field (C-COSMOS), we find suggestive evidence that the AGN fraction increases with local HAE galaxy density. The 2QZ Clus HAEs reside in a moderately overdense environment (a factor of {approx}2 times over the field), and after excluding optically-selected QSOs, we find that the AGN fraction is a factor of {approx}3.5^+3.8^_-2.2_ times higher than C-COSMOS HAEs in similar environments. Using stacking analyses of the Chandra data and Herschel SPIRE observations at 250{mu}m, we respectively estimate mean SMBH accretion rates ((dM/dt)_BH_) and star formation rates (SFRs) for the 2QZ Clus and C-COSMOS samples.
- ID:
- ivo://CDS.VizieR/J/ApJ/766/88
- Title:
- Chandra observations of X-ray binaries in Cen A
- Short Name:
- J/ApJ/766/88
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a spectral investigation of X-ray binaries (XBs) in NGC 5128 (Cen A), using six 100ks Chandra observations taken over two months in 2007. We divide our sample into thermally and non-thermally dominated states based on the behavior of the fitted absorption column N_H_, and present the spectral parameters of sources with L_x_>~2x10^37^erg/s. The majority of sources are consistent with being neutron star low-mass X-ray binaries (NS LMXBs) and we identify three transient black hole (BH) LMXB candidates coincident with the dust lane, which is the remnant of a small late-type galaxy. Our results also provide tentative support for the apparent "gap" in the mass distribution of compact objects between ~2-5M_{sun}_. We propose that BH LMXBs are preferentially found in the dust lane, and suggest this is because of the younger stellar population. The majority (~70%-80%) of potential Roche lobe filling donors in the Cen A halo are >~12Gyr old, while BH LMXBs require donors >~1M_{sun}_ to produce the observed peak luminosities. This requirement for more massive donors may also explain recent results that claim a steepening of the X-ray luminosity function with age at L_x_>=5x10^38^erg/s for the XB population of early-type galaxies; for older stellar populations, there are fewer stars >~1M_{sun}_, which are required to form the more luminous sources.
- ID:
- ivo://CDS.VizieR/J/ApJ/819/162
- Title:
- Chandra obs. of ultracompact dwarf galaxies (UCDs)
- Short Name:
- J/ApJ/819/162
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the first comprehensive archival study of the X-ray properties of ultracompact dwarf (UCD) galaxies, with the goal of identifying weakly accreting central black holes in UCDs. Our study spans 578 UCDs distributed across 13 different host systems, including clusters, groups, fossil groups, and isolated galaxies. Of the 336 spectroscopically confirmed UCDs with usable archival Chandra imaging observations, 21 are X-ray-detected. Imposing a completeness limit of L_X_>2x10^38^erg/s, the global X-ray detection fraction for the UCD population is ~3%. Of the 21 X-ray-detected UCDs, seven show evidence of long-term X-ray time variability on the order of months to years. X-ray-detected UCDs tend to be more compact than non-X-ray-detected UCDs, and we find tentative evidence that the X-ray detection fraction increases with surface luminosity density and global stellar velocity dispersion. The X-ray emission of UCDs is fully consistent with arising from a population of low-mass X-ray binaries (LMXBs). In fact, there are fewer X-ray sources than expected using a naive extrapolation from globular clusters. Invoking the fundamental plane of black hole activity for SUCD1 near the Sombrero galaxy, for which archival Jansky Very Large Array imaging at 5GHz is publicly available, we set an upper limit on the mass of a hypothetical central black hole in that UCD to be <~10^5^M_{sun}_. While the majority of our sources are likely LMXBs, we cannot rule out central black holes in some UCDs based on X-rays alone, and so we address the utility of follow-up radio observations to find weakly accreting central black holes.
- ID:
- ivo://CDS.VizieR/J/ApJS/239/13
- Title:
- Chandra PHAT X-ray catalog of the M31 disk
- Short Name:
- J/ApJS/239/13
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The X-ray source populations within galaxies are typically difficult to identify and classify with X-ray data alone. We are able to break through this barrier by combining deep new Chandra ACIS-I observations with extensive Hubble Space Telescope (HST) imaging from the Panchromatic Hubble Andromeda Treasury of the M31 disk. We detect 373 X-ray sources down to 0.35-8.0keV flux of 10^-15^erg/cm^-2^/s over 0.4deg^2^, 170 of which are reported for the first time. We identify optical counterpart candidates for 188 of the 373 sources, after using the HST data to correct the absolute astrometry of our Chandra imaging to 0.1". While 58 of these 188 are associated with point sources potentially in M31, over half (107) of the counterpart candidates are extended background galaxies, 5 are star clusters, 12 are foreground stars, and 6 are supernova remnants. Sources with no clear counterpart candidate are most likely to be undetected background galaxies and low-mass X-ray binaries in M31. The hardest sources in the 1-8keV band tend to be matched to background galaxies. The 58 point sources that are not consistent with foreground stars are bright enough that they could be high-mass stars in M31; however, all but 8 have optical colors inconsistent with single stars, suggesting that many could be background galaxies or binary counterparts. For point-like counterparts, we examine the star formation history of the surrounding stellar populations to look for a young component that could be associated with a high-mass X-ray binary. About one-third of the point sources are not physically associated with a young population, and are therefore more likely to be background galaxies. For the 40 point-like counterpart candidates associated with young populations, we find that their age distribution has two peaks at 15-20Myr and 40-50Myr. If we only consider the 8 counterpart candidates with typical high-mass main-sequence optical star colors, their age distribution peaks mimic those of the sample of 40. Finally, we find that intrinsic faintness, and not extinction, is the main limitation for finding further counterpart candidates.
- ID:
- ivo://cxc.harvard.edu/csc
- Title:
- Chandra Source Catalog
- Short Name:
- CSC
- Date:
- 24 Oct 2019
- Publisher:
- Chandra X-ray Observatory
- Description:
- The Chandra X-ray Observatory is the U.S. follow-on to the Einstein Observatory and one of NASA"s Great Observatories. Chandra was formerly known as AXAF, the Advanced X-ray Astrophysics Facility, but renamed by NASA in December, 1998. Originally three instruments and a high-resolution mirror carried in one spacecraft, the project was reworked in 1992 and 1993. The Chandra spacecraft carries a high resolution mirror, two imaging detectors, and two sets of transmission gratings. Important Chandra features are: an order of magnitude improvement in spatial resolution, good sensitivity from 0.1 to 10 keV, and the capability for high spectral resolution observations over most of this range. The Chandra Source Catalog (CSC) includes information about X-ray sources detected in observations obtained using the Chandra X-ray Observatory. Release 2.0 of the catalog includes 317,167 point, compact, and extended sources detected in ACIS and HRC-I imaging observations released publicly prior to the end of 2014. Observed source positions and multi-band count rates are reported, as well as numerous derived spatial, photometric, spectral, and temporal calibrated source properties that may be compared with data obtained by other telescopes. Each record includes the best estimates of the properties of a source based on data extracted from all observations in which the source was detected. The Chandra Source Catalog is extracted from the CXC"s Chandra Data Archive (CDA). The CXC should be acknowledged as the source of Chandra data. For detailed information on the Chandra Observatory and datasets see: http://cxc.harvard.edu/ for general Chandra information; http://cxc.harvard.edu/cda/ for the Chandra Data Archive; http://cxc.harvard.edu/csc/ for Chandra Source Catalog information.
- ID:
- ivo://cxc.harvard.edu/csc.siap
- Title:
- Chandra Source Catalog
- Short Name:
- CSC
- Date:
- 24 Oct 2019
- Publisher:
- Chandra X-ray Observatory
- Description:
- The Chandra X-ray Observatory is the U.S. follow-on to the Einstein Observatory. Chandra was formerly known as AXAF, the Advanced X-ray Astrophysics Facility, but renamed by NASA in December, 1998. Originally three instruments and a high-resolution mirror carried in one spacecraft, the project was reworked in 1992 and 1993. The Chandra spacecraft carries a high resolution mirror, two imaging detectors, and two sets of transmission gratings. Important Chandra features are: an order of magnitude improvement in spatial resolution, good sensitivity from 0.1 to 10 keV, and the capability for high spectral resolution observations over most of this range. The Chandra Source Catalog (CSC) includes information about X-ray sources detected in observations obtained using the Chandra X-ray Observatory. Release 2.0 of the catalog includes 317,167 point, compact, and extended sources detected in ACIS and HRC-I imaging observations released publicly prior to the end of 2014. Observed source positions and multi-band count rates are reported, as well as numerous derived spatial, photometric, spectral, and temporal calibrated source properties that may be compared with data obtained by other telescopes. Each record includes the best estimates of the properties of a source based on data extracted from all observations in which the source was detected. The Chandra Source Catalog is extracted from the CXC"s Chandra Data Archive (CDA). The CXC should be acknowledged as the source of Chandra data. For detailed information on the Chandra Observatory and datasets see: http://cxc.harvard.edu/ for general Chandra information; http://cxc.harvard.edu/cda/ for the Chandra Data Archive; http://cxc.harvard.edu/csc/ for Chandra Source Catalog information.
- ID:
- ivo://cxc.harvard.edu/cscr2
- Title:
- Chandra Source Catalog Release 2
- Short Name:
- CSCR2
- Date:
- 24 Oct 2019
- Publisher:
- Chandra X-ray Observatory
- Description:
- The Chandra X-ray Observatory is the U.S. follow-on to the Einstein Observatory and one of NASA"s Great Observatories. Chandra was formerly known as AXAF, the Advanced X-ray Astrophysics Facility, but renamed by NASA in December, 1998. Originally three instruments and a high-resolution mirror carried in one spacecraft, the project was reworked in 1992 and 1993. The Chandra spacecraft carries a high resolution mirror, two imaging detectors, and two sets of transmission gratings. Important Chandra features are: an order of magnitude improvement in spatial resolution, good sensitivity from 0.1 to 10 keV, and the capability for high spectral resolution observations over most of this range. The Chandra Source Catalog (CSC) includes information about X-ray sources detected in observations obtained using the Chandra X-ray Observatory. Release 2.0 of the catalog includes 317,167 point, compact, and extended sources detected in ACIS and HRC-I imaging observations released publicly prior to the end of 2014. Observed source positions and multi-band count rates are reported, as well as numerous derived spatial, photometric, spectral, and temporal calibrated source properties that may be compared with data obtained by other telescopes. Each record includes the best estimates of the properties of a source based on data extracted from all observations in which the source was detected. The Chandra Source Catalog is extracted from the CXC"s Chandra Data Archive (CDA). The CXC should be acknowledged as the source of Chandra data. For detailed information on the Chandra Observatory and datasets see: http://cxc.harvard.edu/ for general Chandra information; http://cxc.harvard.edu/cda/ for the Chandra Data Archive; http://cxc.harvard.edu/csc/ for Chandra Source Catalog information.
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