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2651. Chandra observations of solar analogs
ID:
ivo://CDS.VizieR/J/ApJ/799/163
Title:
Chandra observations of solar analogs
Short Name:
J/ApJ/799/163
Date:
21 Oct 2021
Publisher:
CDS
Description:
We investigate whether magnetic interaction between close-in giant planets and their host stars produce observable statistical enhancements in stellar coronal or chromospheric activity. New Chandra observations of 12 nearby (d<60pc) planet-hosting solar analogs are combined with archival Chandra, XMM-Newton, and ROSAT coverage of 11 similar stars to construct a sample inoculated against inherent stellar class and planet-detection biases. Survival analysis and Bayesian regression methods (incorporating both measurements errors and X-ray upper limits; 13/23 stars have secure detections) are used to test whether "hot Jupiter" hosts are systematically more X-ray luminous than comparable stars with more distant or smaller planets. No significant correlations are present between common proxies for interaction strength (M_P_/a^2^ or 1/a) versus coronal activity (L_X_ or L_X_/L_bol_). In contrast, a sample of 198 FGK main-sequence stars does show a significant (~99% confidence) increase in X-ray luminosity with M_P_/a^2^. While selection biases are incontrovertibly present within the main-sequence sample, we demonstrate that the effect is primarily driven by a handful of extreme hot-Jupiter systems with M_P_/a^2^>450M_Jup_AU^-2^, which here are all X-ray luminous but to a degree commensurate with their Ca II H and K activity, in contrast to presented magnetic star-planet interaction scenarios that predict enhancements relatively larger in L_X_. We discuss these results in the context of cumulative tidal spin-up of stars hosting close-in gas giants (potentially followed by planetary infall and destruction). We also test our main-sequence sample for correlations between planetary properties and UV luminosity or Ca II H and K emission, and find no significant dependence.
2652. Chandra observations of SPT-SZ clusters
ID:
ivo://CDS.VizieR/J/ApJ/774/23
Title:
Chandra observations of SPT-SZ clusters
Short Name:
J/ApJ/774/23
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present first results on the cooling properties derived from Chandra X-ray observations of 83 high-redshift (0.3<z<1.2) massive galaxy clusters selected by their Sunyaev-Zel'dovich signature in the South Pole Telescope data. We measure each cluster's central cooling time, central entropy, and mass deposition rate, and compare these properties to those for local cluster samples. We find no significant evolution from z~0 to z~1 in the distribution of these properties, suggesting that cooling in cluster cores is stable over long periods of time. We also find that the average cool core entropy profile in the inner ~100kpc has not changed dramatically since z~1, implying that feedback must be providing nearly constant energy injection to maintain the observed "entropy floor" at ~10keV cm^2^.
2653. Chandra observations of the 2QZ Cluster 1004+00
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.
2654. Chandra observations of Trumpler 14 and 16
ID:
ivo://CDS.VizieR/J/ApJ/589/509
Title:
Chandra observations of Trumpler 14 and 16
Short Name:
J/ApJ/589/509
Date:
21 Oct 2021
Publisher:
CDS
Description:
The region around the {eta} Carinae Nebula has three OB associations, which contain a Wolf-Rayet star and several massive O3 stars. An early Chandra ACIS-I image was centered on {eta} Car and includes Trumpler 16 and part of Trumpler 14. The Chandra image confirms the well-known result that O and very early B stars are X-ray sources with LX~=10^-7^Lbol over an X-ray luminosity range of about 100. Two new, anomalously strong X-ray sources have been found among the hot star population: Tr 16-244, a heavily reddened O3 I star, and Tr 16-22, a heavily reddened O8.5 V star. Two stars have an unusually large LX/Lbol: HD 93162, a Wolf-Rayet star (and possible binary), and Tr 16-22, a possible colliding-wind binary. In addition, a population of sources associated with cool stars is detected. In the color-magnitude diagram, these X-ray sources sit above the sequence of field stars in the Carina arm. The OB stars are on average more X-ray luminous than the cool star X-ray sources. X-ray sources among A stars have X-ray luminosities similar to those of cooler stars and may be due to cooler companions. Upper limits are presented for B stars that are not detected in X-rays. These upper limits are also the upper limits for any cool companions that the hot stars may have. Hardness ratios are presented for the most luminous sources in bands 0.5-0.9, 0.9-1.5, and 1.5-2.04keV. The available information on the binary nature of the hot stars is discussed, but binarity does not correlate with X-ray strength in a simple way.
2655. Chandra observations of X-ray binaries in Cen A
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.
2656. Chandra obs. of SDSS AGN pairs at z_med_~0.1
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.
2657. Chandra obs. of Serpens star-forming region
ID:
ivo://CDS.VizieR/J/A+A/463/275
Title:
Chandra obs. of Serpens star-forming region
Short Name:
J/A+A/463/275
Date:
21 Oct 2021
Publisher:
CDS
Description:
To study the properties of X-ray emission from young stellar objects (YSOs) through their evolution from Class I to Class III and determine whether Class 0 protostars emit X-rays. A deep Chandra X-ray observation of the Serpens star-forming region was obtained. The Serpens Cloud Core is ideally suited for this type of investigation, being populated by a dense and extremely young cluster whose members are found in all evolutionary stages, including six well-studied Class 0 sources.
2658. Chandra obs. of Trifid nebula
ID:
ivo://CDS.VizieR/J/ApJ/607/904
Title:
Chandra obs. of Trifid nebula
Short Name:
J/ApJ/607/904
Date:
21 Oct 2021
Publisher:
CDS
Description:
The Trifid Nebula, a young star-forming H II region, was observed for 16hr by the ACIS-I detector on board the Chandra X-Ray Observatory. We detected 304 X-ray sources, 30% of which are hard sources and 70% of which have near-infrared counterparts.
2659. 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.
2660. CHANDRA obs. of YSOs in Monoceros R2
ID:
ivo://CDS.VizieR/J/ApJ/567/423
Title:
CHANDRA obs. of YSOs in Monoceros R2
Short Name:
J/ApJ/567/423
Date:
21 Oct 2021
Publisher:
CDS
Description:
We observed the Monoceros R2 molecular cloud with the ACIS-I array on board the Chandra X-Ray Observatory. From the central 3.2'x3.2' region, we detect 154 sources above the detection limit of ~5x10^-16^erg/s/cm^2^ with a 100ks exposure. About 85% of the X-ray sources are identified with an infrared counterpart, including four high-mass stars in the zero-age main-sequence (ZAMS) and/or premain-sequence (PMS) phase. The X-ray spectra of the high-mass ZAMS and PMS stars are represented by a thin thermal plasma model of a temperature above ~2keV. The X-rays are time variable and exhibit rapid flares. This high-temperature plasma and flaring activity is similar to that seen in low-mass PMS stars and is contrary to the behavior observed in high-mass main-sequence stars.The X-ray luminosity increases as the intrinsic K-band flux increases. However, the X-ray luminosity saturates at a level of ~10^31^erg/s. We conclude that high-mass ZAMS and PMS stars emit X-rays, possibly because of magnetic activity such as that of low-mass stars.

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