- ID:
- ivo://CDS.VizieR/J/AJ/145/46
- Title:
- UBVIc photometry in Westerlund 1
- Short Name:
- J/AJ/145/46
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Westerlund 1 is the most important starburst cluster in the Galaxy due to its massive star content. We have performed BVI_C_ and JK_S_ photometry to investigate the initial mass function (IMF). By comparing the observed color with the spectral-type-intrinsic-color relation, we obtain the mean interstellar reddening of <E(B-V)>=4.19+/-0.23 and <E(J-K_S_)>=1.70+/-0.21. Due to the heavy extinction toward the cluster, the zero-age main sequence fitting method based on optical photometry proved to be inappropriate for the distance determination, while the near-infrared photometry gave a reliable distance to the cluster, 3.8kpc from the empirical relation. Using the recent theoretical stellar evolution models with rotation, the age of the cluster is estimated to be 5.0+/-1.0Myr. We derived the IMF in the massive part and obtained a fairly shallow slope of {Gamma}=-0.8+/-0.1. The integration of the IMF gave a total mass for the cluster in excess of 5.0x10^4^M_{sun}_. The IMF shows a clear radial variation indicating the presence of mass segregation. We also discuss the possible star formation history of Westerlund 1 from the presence of red supergiants and relatively low luminosity yellow hypergiants.
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- ID:
- ivo://CDS.VizieR/J/AJ/126/632
- Title:
- UBVRIz'HK' photometry of 2Ms CDFN X-ray sources
- Short Name:
- J/AJ/126/632
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an optical and near-infrared catalog for the X-ray sources in the 2Ms Chandra observation of the Hubble Deep Field North region. We have high-quality multicolor imaging data for all 503 X-ray point sources in the X-ray-selected catalog and reliable spectroscopic redshifts for 284. We spectroscopically identify six high-redshift (z>1) type II quasars (L_2-8keV_>10^44^ergs/s) in our sample. Our spectroscopic completeness for the R<=24 sources is 87%. The spectroscopic redshift distribution shows two broad redshift spikes that have clearly grown over those originally seen in the 1Ms exposure. The spectroscopically identified extragalactic sources already comprise 75% of the measured 2-8keV light. Redshift slices versus 2-8keV flux show that an impressive 54% of the measured 2-8keV light arises from sources at z<1 and 68% from sources at z<2.
- ID:
- ivo://CDS.VizieR/J/A+A/364/205
- Title:
- UBVy photometry of cool stars
- Short Name:
- J/A+A/364/205
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present high-precision photometry, high- and medium-resolution spectroscopy for a sample of 32 stars likely to be the optical counterparts of X-ray sources serendipitously detected by the EXOSAT satellite. Using also recent results from the Hipparcos satellite, we infer spectral types, compute X-ray luminosities and Li abundances and investigate the single or binary nature of the sample stars. We found eleven new variable stars, whose photometric periods fall in the 1.2-27.5 day range, for most of which the optical variability is consistent with the presence of photospheric cool spots. For our sample of X-ray selected stars we confirm the existence of a strong correlation between the stellar rotation rate and the level of activity, and also between the X-ray and bolometric luminosities. Two stars in our sample are likely to be pre-main sequence objects, one is likely to be a previously unknown M-type star within 25pc.
- ID:
- ivo://CDS.VizieR/J/A+A/576/A130
- Title:
- Ultra-deep catalog of X-ray groups in ECDF-S
- Short Name:
- J/A+A/576/A130
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the detection, identification and calibration of extended sources in the deepest X-ray dataset to date, the Extended Chandra Deep Field South (ECDF-S). Ultra-deep observations of ECDF-S with Chandra and XMM-Newton enable a search for extended X-ray emission down to an unprecedented flux of 2x10^-16^ergs/s/cm^2^. By using simulations and comparing them with the Chandra and XMM data, we show that it is feasible to probe extended sources of this flux level, which is 10000 times fainter than the first X-ray group catalogs of the ROSAT all sky survey. Extensive spectroscopic surveys at the VLT and Magellan have been completed, providing spectroscopic identification of galaxy groups to high redshifts. Furthermore, available HST imaging enables a weak-lensing calibration of the group masses. We present the search for the extended emission on spatial scales of 32" in both Chandra and XMM data, covering 0.3 square degrees and model the extended emission on scales of arcminutes. We present a catalog of 46 spectroscopically identified groups, reaching a redshift of 1.6. We show that the statistical properties of ECDF-S, such as logN-logS and X-ray luminosity function are broadly consistent with LCDM, with the exception that dn/dz/d{Omega} test reveals that a redshift range of 0.2<z<0.5 in ECDF-S is sparsely populated. The lack of nearby structure, however, makes studies of high-redshift groups particularly easier both in X-rays and lensing, due to a lower level of clustered foreground. We present one and two point statistics of the galaxy groups as well as weak-lensing analysis to show that the detected low-luminosity systems are indeed low-mass systems. We verify the applicability of the scaling relations between the X-ray luminosity and the total mass of the group, derived for the COSMOS survey to lower masses and higher redshifts probed by ECDF-S by means of stacked weak lensing and clustering analysis, constraining any possible departures to be within 30% in mass. Ultra-deep X-ray surveys uniquely probe the low-mass galaxy groups across a broad range of redshifts. These groups constitute the most common environment for galaxy evolution. Together with the exquisite data set available in the best studied part of the Universe, the ECDF-S group catalog presented here has an exceptional legacy value.
- ID:
- ivo://CDS.VizieR/J/ApJS/235/26
- Title:
- Ultradeep catalog of X-ray point sources in the GC
- Short Name:
- J/ApJS/235/26
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present an updated catalog of X-ray point sources in the inner 500" (~20pc) of the Galactic center (GC), where the nuclear star cluster (NSC) stands, based on a total of ~4.5Ms of Chandra observations taken from 1999 September to 2013 April. This ultradeep data set offers unprecedented sensitivity for detecting X-ray sources in the GC, down to an intrinsic 2-10keV luminosity of 1.0x10^31^erg/s. A total of 3619 sources are detected in the 2-8keV band, among which ~3500 are probable GC sources and ~1300 are new identifications. The GC sources collectively account for ~20% of the total 2-8keV flux from the inner 250" region where detection sensitivity is the greatest. Taking advantage of this unprecedented sample of faint X-ray sources that primarily traces the old stellar populations in the NSC, we revisit global source properties, including long-term variability, cumulative spectra, luminosity function, and spatial distribution. Based on the equivalent width and relative strength of the iron lines, we suggest that in addition to the arguably predominant population of magnetic cataclysmic variables (CVs), nonmagnetic CVs contribute substantially to the detected sources, especially in the lower-luminosity group. On the other hand, the X-ray sources have a radial distribution closely following the stellar mass distribution in the NSC, but much flatter than that of the known X-ray transients, which are presumably low-mass X-ray binaries (LMXBs) caught in outburst. This, together with the very modest long-term variability of the detected sources, strongly suggests that quiescent LMXBs are a minor (less than a few percent) population.
- ID:
- ivo://CDS.VizieR/J/ApJ/739/57
- Title:
- Ultra hard X-ray AGNs in the Swift/BAT survey
- Short Name:
- J/ApJ/739/57
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have assembled the largest sample of ultra hard X-ray selected (14-195keV) active galactic nucleus (AGN) with host galaxy optical data to date, with 185 nearby (z<0.05), moderate luminosity AGNs from the Swift BAT sample. The BAT AGN host galaxies have intermediate optical colors (u-r and g-r) that are bluer than a comparison sample of inactive galaxies and optically selected AGNs from the Sloan Digital Sky Survey (SDSS) which are chosen to have the same stellar mass. Based on morphological classifications from the RC3 and the Galaxy Zoo, the bluer colors of BAT AGNs are mainly due to a higher fraction of mergers and massive spirals than in the comparison samples. BAT AGNs in massive galaxies (logM*>10.5) have a 5-10 times higher rate of spiral morphologies than in SDSS AGNs or inactive galaxies. We also see enhanced far-infrared emission in BAT AGN suggestive of higher levels of star formation compared to the comparison samples. BAT AGNs are preferentially found in the most massive host galaxies with high concentration indexes indicative of large bulge-to-disk ratios and large supermassive black holes. The narrow-line (NL) BAT AGNs have similar intrinsic luminosities as the SDSS NL Seyferts based on measurements of [OIII]5007. There is also a correlation between the stellar mass and X-ray emission. The BAT AGNs in mergers have bluer colors and greater ultra hard X-ray emission compared to the BAT sample as a whole.
- ID:
- ivo://CDS.VizieR/J/ApJS/157/59
- Title:
- Ultraluminous X-ray sources in nearby galaxies
- Short Name:
- J/ApJS/157/59
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- X-ray observations have revealed in other galaxies a class of extranuclear X-ray point sources with X-ray luminosities of 10^39^-10^41^ergs/s, exceeding the Eddington luminosity for stellar mass X-ray binaries. These ultraluminous X-ray sources (ULXs) may be powered by intermediate-mass black holes of a few thousand M_Sun_ or stellar mass black holes with special radiation processes. In this paper, we present a survey of ULXs in 313 nearby galaxies with D_25_>1 within 40Mpc with 467 ROSAT High Resolution Imager (HRI) archival observations. The HRI observations are reduced with uniform procedures, refined by simulations that help define the point source detection algorithm employed in this survey. A sample of 562 extragalactic X-ray point sources with L_X_=10^38^-10^43^ergs/s is extracted from 173 survey galaxies, including 106 ULX candidates within the D_25_ isophotes of 63 galaxies and 110 ULX candidates between 1D_25_ and 2D_25_ of 64 galaxies, from which a clean sample of 109 ULXs is constructed to minimize the contamination from foreground or background objects.
- ID:
- ivo://CDS.VizieR/J/MNRAS/446/470
- Title:
- ULX candidates in luminous infrared galaxies
- Short Name:
- J/MNRAS/446/470
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present results from a Chandra study of ultraluminous X-ray sources (ULXs) in a sample of 17 nearby (D_L_<60Mpc) luminous infrared galaxies (LIRGs), selected to have star formation rates (SFRs) in excess of 7M_{sun}_/yr and low foreground Galactic column densities (N_H_<~5x10^20^cm^-2^). A total of 53 ULXs were detected and we confirm that this is a complete catalogue of ULXs for the LIRG sample. We examine the evolution of ULX spectra with luminosity in these galaxies by stacking the spectra of individual objects in three luminosity bins, finding a distinct change in spectral index at luminosity ~2x10^39^erg/s. This may be a change in spectrum as 10M_{sun}_ black holes transit from an ~ Eddington to a super-Eddington accretion regime, and is supported by a plausible detection of partially ionized absorption imprinted on the spectrum of the luminous ULX (L_X_~5x10^39^erg/s) CXOU J024238.9-000055 in NGC 1068, consistent with the highly ionized massive wind that we would expect to see driven by a super-Eddington accretion flow. This sample shows a large deficit in the number of ULXs detected per unit SFR (0.2 versus 2 ULXs, per M_{sun}_/yr) compared to the detection rate in nearby (D_L_<14.5Mpc) normal star-forming galaxies. This deficit also manifests itself as a lower differential X-ray luminosity function normalization for the LIRG sample than for samples of other star-forming galaxies. We show that it is unlikely that this deficit is a purely observational effect. Part of this deficit might be attributable to the high metallicity of the LIRGs impeding the production efficiency of ULXs and/or a lag between the star formation starting and the production of ULXs; however, we argue that the evidence - including very low N_ULX_/L_FIR_, and an even lower ULX incidence in the central regions of the LIRGs - shows that the main culprit for this deficit is likely to be the high column of gas and dust in these galaxies, that fuels the high SFR but also acts to obscure many ULXs from our view.
- ID:
- ivo://CDS.VizieR/J/AJ/143/144
- Title:
- ULX candidates in nearby Arp galaxies
- Short Name:
- J/AJ/143/144
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have conducted a statistical analysis of the ultra-luminous X-ray point sources (ULXs; L_X_>=10^39^erg/s) in a sample of galaxies selected from the Arp Atlas of Peculiar Galaxies (1996, Cat. VII/192; Webb, 1996, Cat. VII/192). We find a possible enhancement of a factor of ~2-4 in the number of ULXs per blue luminosity for the strongly interacting subset. Such an enhancement would be expected if ULX production is related to star formation, as interacting galaxies tend to have enhanced star formation rates on average. For most of the Arp galaxies in our sample, the total number of ULXs compared to the far-infrared luminosity is consistent with values found earlier for spiral galaxies. This suggests that for these galaxies, ULXs trace recent star formation. However, for the most infrared-luminous galaxies, we find a deficiency of ULXs compared to the infrared luminosity. For these very infrared-luminous galaxies, active galactic nuclei may contribute to powering the far-infrared; alternatively, ULXs may be highly obscured in the X-ray in these galaxies and therefore not detected by these Chandra observations. We determined local UV/optical colors within the galaxies in the vicinity of the candidate ULXs using Galaxy Evolution Explorer UV and Sloan Digitized Sky Survey optical images. In most cases, the distributions of colors are similar to the global colors of interacting galaxies. However, the u-g and r-i colors at the ULX locations tend to be bluer on average than these global colors, suggesting that ULXs are preferentially found in regions with young stellar populations. In the Arp sample there is a possible enhancement of a factor of ~2-5 in the fraction of galactic nuclei that are X-ray-bright compared to more normal spirals.
- ID:
- ivo://CDS.VizieR/J/ApJ/741/49
- Title:
- ULX candidates in nearby galaxies
- Short Name:
- J/ApJ/741/49
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One hundred seven ultraluminous X-ray sources (ULXs) with 0.3-10.0keV luminosities in excess of 10^39^erg/s are identified in a complete sample of 127 nearby galaxies. The sample includes all galaxies within 14.5Mpc above the completeness limits of both the Uppsala Galaxy Catalogue (Cat. VII/26) and the Infrared Astronomical Satellite survey (Cat. II/125). The galaxy sample spans all Hubble types, a four-decade range in mass, 7.5<log(M/M_{sun}_)<11.4, and in star formation rate, 0.0002<SFR(M_{sun}_/yr)<=3.6. ULXs are detected in this sample at rates of one per 3.2x10^10^M_{sun}_, one per ~0.5M_{sun}_/yr star formation rate, and one per 57Mpc^3^ corresponding to a luminosity density of ~2x10^37^erg/s/Mpc^3^. At these rates we estimate as many as 19 additional ULXs remain undetected in fainter dwarf galaxies within the survey volume. An estimated 14 objects, or 13%, of the 107 ULX candidates are expected to be background sources. The differential ULX luminosity function shows a power-law slope {alpha}~-0.8 to -2.0 with an exponential cutoff at ~20x10^39^erg/s with precise values depending on the model and on whether the ULX luminosities are estimated from their observed numbers of counts or, for a subset of candidates, from their spectral shapes. Extrapolating the observed luminosity function predicts at most one very luminous ULX, L_X_~10^41^erg/s, within a distance as small as 100Mpc. The luminosity distribution of ULXs within the local universe cannot account for the recent claims of luminosities in excess of 2x10^41^erg/s, requiring a new population class to explain these extreme objects.
