- ID:
- ivo://CDS.VizieR/J/ApJS/204/14
- Title:
- Deep Chandra observations of NGC 4649. I.
- Short Name:
- J/ApJS/204/14
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the X-ray source catalog for the Chandra monitoring observations of the elliptical galaxy, NGC 4649 (M60). The galaxy has been observed with Chandra ACIS-S3 in six separate pointings, reaching a total exposure of 299ks. There are 501 X-ray sources detected in the 0.3-8.0keV band in the merged observation or in one of the six individual observations; 399 sources are located within the D_25_ ellipse. The observed 0.3-8.0keV luminosities of these 501 sources range from 9.3x10^36^erg/s to 5.4x10^39^erg/s. The 90% detection completeness limit within the D_25_ ellipse is 5.5x10^37^erg/s. Based on the surface density of background active galactic nuclei (AGNs) and detection completeness, we expect ~45 background AGNs among the catalog sources (~15 within the D_25_ ellipse). There are nine sources with luminosities greater than 10^39^erg/s, which are candidates for ultraluminous X-ray sources. The nuclear source of NGC 4649 is a low-luminosity AGN, with an intrinsic 2.0-8.0keV X-ray luminosity of 1.5x10^38^erg/s. The X-ray colors suggest that the majority of the catalog sources are low-mass X-ray binaries (LMXBs). We find that 164 of the 501 X-ray sources show long-term variability, indicating that they are accreting compact objects. We discover four transient candidates and another four potential transients. We also identify 173 X-ray sources (141 within the D_25_ ellipse) that are associated with globular clusters (GCs) based on Hubble Space Telescope and ground-based data; these LMXBs tend to be hosted by red GCs. Although NGC 4649 has a much larger population of X-ray sources than the structurally similar early-type galaxies, NGC 3379 and NGC 4278, the X-ray source properties are comparable in all three systems.
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- ID:
- ivo://CDS.VizieR/J/ApJS/213/23
- Title:
- Deep Chandra obs. of the giant HII region N11 in LMC
- Short Name:
- J/ApJS/213/23
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- A very sensitive X-ray investigation of the giant H II region N11 in the Large Megallanic Cloud was performed using the Chandra X-ray Observatory. The 300ks observation reveals X-ray sources with luminosities down to 10^32^erg/s, increasing the number of known point sources in the field by more than a factor of five. Among these detections are 13 massive stars (3 compact groups of massive stars, 9 O stars, and one early B star) with log (L_X_/L_BOL_)~-6.5 to -7, which may suggest that they are highly magnetic or colliding-wind systems. On the other hand, the stacked signal for regions corresponding to undetected O stars yields log (L_X_/L_BOL_)~-7.3, i.e., an emission level comparable to similar Galactic stars despite the lower metallicity. Other point sources coincide with 11 foreground stars, 6 late-B/A stars in N11, and many background objects. This observation also uncovers the extent and detailed spatial properties of the soft, diffuse emission regions, but the presence of some hotter plasma in their spectra suggests contamination by the unresolved stellar population.
- ID:
- ivo://CDS.VizieR/J/ApJ/862/73
- Title:
- Deep Chandra obs. of X-ray point sources in M87
- Short Name:
- J/ApJ/862/73
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a study of X-ray source populations in M87, the cD galaxy of the Virgo cluster, using 12 archival Chandra observations with a total exposure of ~680ks spanning about a decade. A total of 346 point-like sources are detected down to a limiting 0.5-8keV luminosity of 4x10^37^erg/s and out to a galactocentric radius of ~40kpc. We cross-correlate the X-ray sources with published catalogs of globular clusters (GCs), derived from the ACS Virgo Cluster Survey and the Next Generation Virgo Cluster Survey. This results in 122 matches, making it one of the largest samples of GC-hosting X-ray sources in an external galaxy. These sources, most likely low-mass X-ray binaries (LMXBs), correspond to ~5% of all known GCs within the Chandra field-of-view. Conversely, ~50% of the detected X-ray sources are found in a GC. Moreover, red (metal-rich) GCs are ~2.2 times more likely to host an X-ray source than blue (metal-poor) GCs. We also examine 76 currently known ultra-compact dwarf galaxies around M87 but find no significant X-ray counterparts. After statistically accounting for the cosmic X-ray background, we identify ~110 field-LMXBs. The GC-LMXBs and field-LMXBs differ in their luminosity function and radial distribution, which indicates that the latter cannot be primarily originated from GCs. Using another set of deep Chandra observations toward ~100kpc northwest of the M87 center, we statistically constrain the abundance of field-LMXBs in the stellar halo, which is consistent with that found in the central region. We also identify 40 variable X-ray sources, among which one source is likely a black hole binary residing in a GC.
- ID:
- ivo://CDS.VizieR/J/A+A/637/A52
- Title:
- Deep Chandra survey in J1030+0524 field
- Short Name:
- J/A+A/637/A52
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the X-ray source catalog for the 479ks Chandra exposure of the SDSS J1030+0524 field, that is centered on a region that shows the best evidence to date of an overdensity around a z>6 quasar, and also includes a galaxy overdensity around a Comptonthick Fanaro-Riley type II (FRII) radio galaxy at z=1.7. Using wavdetect for initial source detection and ACIS Extract for source photometry and significance assessment, we create preliminary catalogs of sources that are detected in the full (0.5-7.0keV), soft (0.5-2.0keV), and hard (2-7keV) bands, respectively. We produce X-ray simulations that mirror our Chandra observation to filter our preliminary catalogs and get a completeness level of > 91% and a reliability level of 95% in each band. The catalogs in the three bands are then matched into a final main catalog of 256 unique sources. Among them, 244, 193, and 208 are detected in the full, soft, and hard bands, respectively. The Chandra observation covers a total area of 335 arcmin2, and reaches flux limits over the central few square arcmins of ~3x10^-16^, 6x10^-17^, and 2x10^-16^erg/cm2/s in the full, soft, and hard bands, respectively This makes J1030 field the fifth deepest extragalactic X-ray survey to date. The field is part of the Multiwavelength Survey by Yale-Chile (MUSYC), and is also covered by optical imaging data from the Large Binocular Camera (LBC) at the Large Binocular Telescope (LBT), near-IR imaging data from the Canada France Hawaii Telescope WIRCam (CFHT/WIRCam), and Spitzer IRAC. Thanks to its dense multi-wavelength coverage, J1030 represents a legacy field for the study of large-scale structures around distant accreting supermassive black holes. Using a likelihood ratio analysis, we associate multi-band (r, z, J, and 4.5um) counterparts for 252 (98.4%) of the 256 Chandra sources, with an estimated reliability of 95%. Finally, we compute the cumulative number of sources in each X-ray band, finding that they are in general agreement with the results from the Chandra Deep Fields.
- ID:
- ivo://CDS.VizieR/J/MNRAS/356/568
- Title:
- Deep Chandra survey of the Groth Strip
- Short Name:
- J/MNRAS/356/568
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a 200-ks Chandra observation of part of the Groth Strip region, using the ACIS-I instrument. We present a relatively simple method for the detection of point sources and calculation of limiting sensitivities, which we argue is at least as sensitive and more self-consistent than previous methods presented in the literature. A total of 158 distinct X-ray sources are included in our point-source catalogue in the ACIS-I area. The number counts show a relative dearth of X-ray sources in this region.
- ID:
- ivo://CDS.VizieR/J/MNRAS/371/221
- Title:
- Deep Chandra survey of the Groth Strip. II.
- Short Name:
- J/MNRAS/371/221
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- In this paper, we discuss the optical and X-ray spectral properties of the sources detected in a single 200-ks Chandra pointing in the Groth-Westphal Strip region. A wealth of optical photometric and spectroscopic data are available in this field providing optical identifications and redshift determinations for the X-ray population. The optical photometry and spectroscopy used here are primarily from the Deep Extragalactic Evolutionary Probe 2 (DEEP2) survey with additional redshifts obtained from the literature. These are complemented with the deeper (r>>26mag) multiwaveband data (ugriz) from the Canada-France-Hawaii Telescope Legacy Survey to estimate photometric redshifts and to optically identify sources fainter than the DEEP2 magnitude limit (R_AB_>>24.5mag). We focus our study on the 2-10keV selected sample comprising 97 sources to the limit 8x10^-16^erg/s/cm^2^, this being the most complete in terms of optical identification rate (86 per cent) and redshift determination fraction (63 per cent; both spectroscopic and photometric).
- ID:
- ivo://CDS.VizieR/J/ApJ/887/20
- Title:
- Deep Chandra survey of the SMC. III. HMXBs
- Short Name:
- J/ApJ/887/20
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have compiled the most complete census of high-mass X-ray binaries (HMXBs) in the Small Magellanic Cloud with the aim to investigate the formation efficiency of young accreting binaries in its low-metallicity environment. In total, we use 123 X-ray sources with detections in our Chandra X-ray Visionary Program (XVP), supplemented by 14 additional (likely and confirmed) HMXBs identified by Haberl & Sturm (2016, J/A+A/586/A81) that fall within the XVP area, but are neither detected in our survey (nine sources) nor matched with any of the 127 sources identified in the XVP data (five sources). Specifically, we examine the number ratio of the HMXBs [N(HMXBs)] to (a) the number of OB stars, (b) the local star formation rate (SFR), and (c) the stellar mass produced during the specific star formation burst, all as a function of the age of their parent stellar populations. Each of these indicators serves a different role, but in all cases we find that the HMXB formation efficiency increases as a function of time (following a burst of star formation) up to ~40-60Myr, and then gradually decreases. The formation efficiency peaks at ~30-40Myr with average rates of N(HMXB)/SFR=339_-83_^+78^(M_{sun}_/yr)^-1^, and N(HMXB)/M*=(8.74_-0.92_^+1.0^)x10^-6^M_{sun}_^-1^, in good agreement with previous estimates of the average formation efficiency in the broad ~20-60Myr age range.
- ID:
- ivo://CDS.VizieR/J/A+A/396/397
- Title:
- Deep cluster survey in Chandra archival data
- Short Name:
- J/A+A/396/397
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- I present the first results of a search for clusters of galaxies in Chandra ACIS pointed observations at high galactic latitude with exposure times larger than 10ks. The survey is being carried out using the Voronoi Tessellation and Percolation technique, which is particularly suited for the detection and accurate quantification of extended and/or low surface brightness emission in X-ray imaging observations. A new catalogue of 36 cluster candidates has been created from 5.55deg^2^ of surveyed area. Five of these candidates have already been associated to visible enhancements of the projected galaxy distribution in low deepness DSS-II fields and are probably low-to moderate redshift systems. Three of the candidates have been identified in previous ROSAT-based surveys. I show that a significative fraction (30-40%) of the candidate clusters are probably intermediate to high redshift systems. In this paper I publish the catalogue of these first candidate clusters. I also derive the number counts of clusters and compare it with the results of deep ROSAT-based cluster surveys.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/2606
- Title:
- Deep echelle spectrophotometry of NGC3918
- Short Name:
- J/MNRAS/452/2606
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The chemical content of the planetary nebula NGC 3918 is investigated through deep, high-resolution (R~40000) UVES (Ultraviolet-Visual Echelle Spectrograph) at VLT (Very Large Telescope) spectrophotometric data. We identify and measure more than 750 emission lines, making ours one of the deepest spectra ever taken for a planetary nebula. Among these lines we detect very faint lines of several neutron-capture elements (Se, Kr, Rb, and Xe), which enable us to compute their chemical abundances with unprecedented accuracy, thus constraining the efficiency of the s-process and convective dredge-up in NGC 3918 progenitor star. We find that Kr is strongly enriched in NGC 3918 and that Se is less enriched than Kr, in agreement with the results of previous papers and with predicted s-process nucleosynthesis. We also find that Xe is not as enriched by the s-process in NGC 3918 as is Kr and, therefore, that neutron exposure is typical of modestly subsolar metallicity asymptotic giant branch (AGB) stars. A clear correlation is found when representing [Kr/O] versus log(C/O) for NGC 3918 and other objects with detection of multiple ions of Kr in optical data, confirming that carbon is brought to the surface of AGB stars along with s-processed material during third dredge-up episodes, as predicted by nucleosynthesis models. We also detect numerous refractory element lines (Ca, K, Cr, Mn, Fe, Co, Ni, and Cu) and a large number of metal recombination lines of C, N, O, and Ne. We compute physical conditions from a large number of diagnostics, which are highly consistent among themselves assuming a three-zone ionization scheme. Thanks to the high ionization of NGC 3918 we detect a large number of recombination lines of multiple ionization stages of C, N, O and Ne. The abundances obtained for these elements by using recently determined state-of-the-art ionization correction factor (ICF) schemes or simply adding ionic abundances are in very good agreement, demonstrating the quality of the recent ICF scheme for high-ionization planetary nebulae.
- ID:
- ivo://CDS.VizieR/J/ApJ/654/915
- Title:
- Deep FORS1 BR photometry of omega Cen
- Short Name:
- J/ApJ/654/915
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of a deep photometric survey performed with the VLT FORS1 aimed at investigating the complex main-sequence structure of the stellar system Centauri. We confirm the presence of a double main sequence and identify its blue component (bMS) over a large field of view up to 26' from the cluster center. We found that bMS stars are significantly more concentrated toward the cluster center than the other "normal" MS stars. The bMS morphology and its position in the CMD have been used to constrain the helium overabundance required to explain the observed MS morphology.