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581. Chandra obs. of ultracompact dwarf galaxies (UCDs)
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.
582. Chandra PHAT X-ray catalog of the M31 disk
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.
583. Chandra X-ray observations of M81
ID:
ivo://CDS.VizieR/J/ApJS/144/213
Title:
Chandra X-ray observations of M81
Short Name:
J/ApJS/144/213
Date:
21 Oct 2021
Publisher:
CDS
Description:
A Chandra X-Ray Observatory ACIS-S imaging observation is used to study the population of X-ray sources in the nearby Sab galaxy M81 (NGC 3031). A total of 177 sources are detected with 124 located within the D_25_ isophote to a limiting X-ray luminosity of ~3x10^36^erg/s. Source positions, count rates, luminosities in the 0.3-8.0 keV band, limiting optical magnitudes, and potential counterpart identifications are tabulated. Spectral and timing analysis of the 36 brightest sources are reported including the low-luminosity active galactic nucleus, SN 1993J, and the Einstein-discovered ultraluminous X-ray source X6.
584. Chandra X-ray observations of NGC 1316
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).
585. Chandra X-ray point sources in nearby 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.
586. Chandra X-ray point sources of NGC 300
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.
587. Chandra X-ray sources of NGC 1068
ID:
ivo://CDS.VizieR/J/ApJ/591/138
Title:
Chandra X-ray sources of NGC 1068
Short Name:
J/ApJ/591/138
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present an analysis of the compact X-ray source population in the Seyfert 2 galaxy NGC 1068, imaged with a 50ks Chandra observation. We find a total of 84 compact sources on the S3 chip, of which 66 are located within the 25.0B-mag/arcsec^2^ isophote of the galactic disk of NGC 1068. Spectra have been obtained for the 21 sources with at least 50 counts and modeled with both multicolor disk blackbody and power-law models.
588. Chandra X-ray sources of NGC 1399
ID:
ivo://CDS.VizieR/J/ApJ/736/90
Title:
Chandra X-ray sources of NGC 1399
Short Name:
J/ApJ/736/90
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a wide-field study of the globular cluster (GC)/low-mass X-ray binary (LMXB) connection in the giant elliptical NGC 1399. The large field of view of the Advanced Camera for Surveys/WFC, combined with Hubble Space Telescope and Chandra high resolution, allow us to constrain the LMXB formation scenarios in elliptical galaxies. We confirm that NGC 1399 has the highest LMXB fraction in GCs of all nearby elliptical galaxies studied so far, even though the exact value depends on galactocentric distance due to the interplay of a differential GC versus galaxy light distribution and the GC color dependence. In fact, LMXBs are preferentially hosted by bright, red GCs out to >5R_eff_ of the galaxy light. The finding that GCs hosting LMXBs follow the radial distribution of their parent GC population argues against the hypothesis that the external dynamical influence of the galaxy affects the LMXB formation in GCs. On the other hand, field-LMXBs closely match the host galaxy light, thus indicating that they are originally formed in situ and not inside GCs. We measure GC structural parameters, finding that the LMXB formation likelihood is influenced independently by mass, metallicity, and GC structural parameters. In particular, the GC central density plays a major role in predicting which GCs host accreting binaries. Finally, our analysis shows that LMXBs in GCs are marginally brighter than those in the field, and in particular the only color-confirmed GC with L_X_>10^39^erg/s shows no variability, which may indicate a superposition of multiple LMXBs in these systems.
589. CHANG-ES. IV. VLA D-configuration observations
ID:
ivo://CDS.VizieR/J/AJ/150/81
Title:
CHANG-ES. IV. VLA D-configuration observations
Short Name:
J/AJ/150/81
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the first part of the observations made for the Continuum Halos in Nearby Galaxies, an EVLA Survey (CHANG-ES) project. The aim of the CHANG-ES project is to study and characterize the nature of radio halos, their prevalence as well as their magnetic fields, and the cosmic rays illuminating these fields. This paper reports observations with the compact D configuration of the Karl G. Jansky Very Large Array (VLA) for the sample of 35 nearby edge-on galaxies of CHANG-ES. With the new wide bandwidth capabilities of the VLA, an unprecedented sensitivity was achieved for all polarization products. The beam resolution is an average of 9.6" and 36" with noise levels reaching approximately 6 and 30{mu}Jy/beam for C- and L-bands, respectively (robust weighting). We present intensity maps in these two frequency bands (C and L), with different weightings, as well as spectral index maps, polarization maps, and new measurements of star formation rates (SFRs). The data products described herein are available to the public in the CHANG-ES data release available at http://www.queensu.ca/changes. We also present evidence of a trend among galaxies with larger halos having higher SFR surface density, and we show, for the first time, a radio continuum image of the median galaxy, taking advantage of the collective signal-to-noise ratio of 30 of our galaxies. This image shows clearly that a "typical" spiral galaxy is surrounded by a halo of magnetic fields and cosmic rays.
590. CHAOS IV: NGC3184 LBT obs. & 3 other gal. abundances
ID:
ivo://CDS.VizieR/J/ApJ/893/96
Title:
CHAOS IV: NGC3184 LBT obs. & 3 other gal. abundances
Short Name:
J/ApJ/893/96
Date:
07 Mar 2022 07:28:28
Publisher:
CDS
Description:
The chemical abundances of spiral galaxies, as probed by HII regions across their disks, are key to understanding the evolution of galaxies over a wide range of environments. We present Large Binocular Telescope/Multi-Object Double Spectrographs spectra of 52 HII regions in NGC 3184 as part of the CHemical Abundances Of Spirals (CHAOS) project. We explore the direct-method gas-phase abundance trends for the first four CHAOS galaxies, using temperature measurements from one or more auroral-line detections in 190 individual HII regions. We find that the dispersion in T_e_-T_e_ relationships is dependent on ionization, as characterized by F_{lambda}5007_/F_{lambda}3727_, and so we recommend ionization-based temperature priorities for abundance calculations. We confirm our previous results that [NII] and [SIII] provide the most robust measures of electron temperature in low-ionization zones, while [OIII] provides reliable electron temperatures in high-ionization nebula. We measure relative and absolute abundances for O, N, S, Ar, and Ne. The four CHAOS galaxies marginally conform with a universal O/H gradient, as found by empirical integral field unit studies when plotted relative to effective radius. However, after adjusting for vertical offsets, we find a tight universal N/O gradient of {alpha}_N/O_=-0.33dex/R_e_ with {sigma}_tot._=0.08 for R_g_/R_e_<2.0, where N is dominated by secondary production. Despite this tight universal N/O gradient, the scatter in the N/O-O/H relationship is significant. Interestingly, the scatter is similar when N/O is plotted relative to O/H or S/H. The observable ionic states of S probe lower ionization and excitation energies than O, which might be more appropriate for characterizing abundances in metal-rich HII regions.