- ID:
- ivo://CDS.VizieR/J/ApJ/690/644
- Title:
- Properties of SDSS QSOs in the ChaMP
- Short Name:
- J/ApJ/690/644
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We study the spectral energy distributions and evolution of a large sample of optically selected quasars from the Sloan Digital Sky Survey that were observed in 323 Chandra images analyzed by the Chandra Multiwavelength Project. Our highest-confidence matched sample includes 1135 X-ray detected quasars in the redshift range 0.2<z<5.4, representing some 36Msec of effective exposure. We provide catalogs of QSO properties, and describe our novel method of calculating X-ray flux upper limits and effective sky coverage. Spectroscopic redshifts are available for about 1/3 of the detected sample; elsewhere, redshifts are estimated photometrically. We detect 56 QSOs with redshift z>3, substantially expanding the known sample. We find no evidence for evolution out to z~5 for either the X-ray photon index {Gamma} or for the ratio of optical/UV to X-ray flux {alpha}_ox_.
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Search Results
- ID:
- ivo://CDS.VizieR/J/ApJS/154/519
- Title:
- Properties of ultraluminous X-ray candidates
- Short Name:
- J/ApJS/154/519
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- One hundred fifty-four (actually 155) discrete non-nuclear ultraluminous X-ray (ULX) sources, with spectroscopically determined intrinsic X-ray luminosities greater than 10^39^erg/s, are identified in 82 galaxies observed with Chandra's Advanced CCD Imaging Spectrometer (ACIS). Source positions, X-ray luminosities, and spectral and timing characteristics are tabulated.
- ID:
- ivo://CDS.VizieR/J/ApJ/696/580
- Title:
- Properties of weak emission-line QSOs (WLQ)
- Short Name:
- J/ApJ/696/580
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present Chandra observations of nine high-redshift quasars (z=2.7-5.9) discovered by the Sloan Digital Sky Survey with weak or undetectable high-ionization emission lines in their UV spectra (WLQs). Adding archival X-ray observations of six additional sources of this class has enabled us to place the strongest constraints yet on the X-ray properties of this remarkable class of active galactic nuclei (AGNs). Although our data cannot rule out the possibility that the emission lines are overwhelmed by a relativistically boosted continuum, as manifested by BL Lac objects, we find that WLQs are considerably weaker in the X-ray and radio bands than the majority of BL Lacs found at much lower redshifts. If WLQs are high-redshift BL Lacs, then it is difficult to explain the lack of a large parent population of X-ray and radio bright weak-lined sources at high redshift. We also consider the possibility that WLQs are quasars with extreme properties, and in particular that the emission lines are suppressed by high accretion rates. Using joint spectral fitting of the X-ray spectra of 11 WLQs, we find that the mean photon index in the hard X-ray band is consistent with those observed in typical radio-quiet AGNs with no hint of an unusually steep hard-X-ray spectrum. This result poses a challenge to the hypothesis that WLQs have extremely high accretion rates, and we discuss additional observations required to test this idea.
- ID:
- ivo://CDS.VizieR/J/A+A/525/A127
- Title:
- Properties of X-ray selected AGNs
- Short Name:
- J/A+A/525/A127
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- There is mounting evidence that active galactic nuclei (AGN) selected through optical emission lines or radio luminosities comprise two distinct AGN populations, whose activity is triggered by different processes. In two previous papers, we studied the host galaxies and environment of radio-loud AGN. In this third paper we study the properties of a sample of Type-2 AGN that were selected on the basis of their [2-10]keV X-ray luminosity. We find that the X-ray luminosity function is in good agreement with previous studies and that the fraction of galaxies hosting an X-ray AGN is a strong function of the stellar mass of the host galaxy. The shape of this fraction-mass relation is similar to the fraction of galaxies that are emission-line AGN, while it differs significantly from the relation observed for radio-selected AGN. The AGN in our sample tend to be located in underdense environments where galaxy mergers and interactions are likely to occur. For all host galaxy masses, the Type-2 AGN display a strong infrared excess at short (~3.5um) wavelengths, suggesting the presence of hot dust possibly associated with a hot dusty torus. These results add weight to the belief that the X-ray selection criteria identifies a population of AGN similar to the emission-line selected population but distinct from the radio population at high masses.
- ID:
- ivo://CDS.VizieR/J/A+A/451/835
- Title:
- Properties of X-ray sources in M31/M33
- Short Name:
- J/A+A/451/835
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have obtained optical spectra for the 14 brightest optical counterparts of X-ray sources identified by XMM-Newton in the direction of M 31 and for 21 optical counterparts in the direction of M 33, using the 1.3m Skinakas telescope in Crete, Greece.
- ID:
- ivo://CDS.VizieR/J/A+A/427/387
- Title:
- QORG catalog of radio/X-ray sources
- Short Name:
- J/A+A/427/387
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The QUASARS.ORG Catalogues align and overlay the year 2001/2 releases of the ROSAT HRI, RASS, PSPC and WGA X-ray catalogues, the NVSS (2002), FIRST (2003) and SUMSS (2003) radio catalogues, the Veron QSO catalogue (2003) and various galaxy/star reference catalogues onto the optical APM and USNO-A catalogues. These catalogues display calculated percentage probabilities for each optical radio/X-ray associated object of its likelihood of being a quasar, galaxy, star, or erroneous radio/X-ray association. The main Master catalogue (master.dat) displays all 501,761 radio/X-ray associated optical objects and known quasars which are optically detected in APM/USNO-A. Up to six radio/X-ray catalog identifications are presented for each optical object, plus any double radio lobes (21,498 of these). These are superimposed (and laterally fitted) onto a 670,925,779-object optical background which combines APM and USNO-A data. The Free-Lunch catalogue is a concise easy-to-read variant of the Master catalogue showcasing just one X-ray and/or radio identification for each object. This catalogue is the original version which was publicized to show astronomers that there *is* a free lunch after all! There is also a subset catalogue of QSO candidates, and a subset catalogue of known QSOs/galaxies/stars. Objects presented in this catalogue are those optical APM/USNO-A objects which are associated with X-ray/radio detections, or any optically-found catalogued QSO/AGN/Bl Lac objects, with confidence >40% of being a radio/X-ray emitting optical object. There are 501,761 objects included in all (including 48,285 catalogued quasars), representing the 99.4% coverage of the sky available from the APM and USNO-A. Each object is shown as one line bearing the position in equatorial coordinates, red and blue optical magnitudes (recalibrated) and PSF class, calculated probabilities of the object being, separately, a quasar, galaxy, star, or erroneous radio/X-ray association, any radio identification from each of the NVSS, FIRST and SUMSS surveys, including candidate double-lobe detections, any X-ray identification from each of the ROSAT HRI, RASS, PSPC and WGA surveys, including fluxes and field shifts of those identifications, plus, if already catalogued, the object name and redshift where applicable. The QORG catalogue and supporting data can be accessed from the catalogue home page at http://quasars.org/qorg-data.htm Questions or comments may be directed to eric@flesch.org
- ID:
- ivo://CDS.VizieR/J/ApJ/747/107
- Title:
- QSO Candidates in the MACHO LMC database
- Short Name:
- J/ApJ/747/107
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a catalog the 2566 QSO candidates in the MACHO LMC database. In these catalogs, we complied number of properties of the objects including RA, Dec, crossmatched IDs with several catalogs, magnitudes, photometric redshifts, etc. See Kim et al. (2011ApJ...735...68K) for the SVM (a.k.a. Support Vector Machine, a supervised machine learning algorithm) QSO classification model based on the time variability of lightcurves. We used the model to select the 2566 QSO candidates. In this work, we employed multiple diagnostics such as X-ray flux, mid-IR color and AGN SED fitting in order to select 663 promising QSO candidates among the 2,566 candidates. These candidates are flagged in the catalog. We calibrated the MACHO RA and Dec of the candidates using the UCAC3 catalog and improved the average astrometric accuracy from ~3" to ~0.5".
- ID:
- ivo://CDS.VizieR/J/A+A/642/A150
- Title:
- Quasars as standard candles. III.
- Short Name:
- J/A+A/642/A150
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalogue of ~2400 optically selected quasars with spectroscopic redshifts and X-ray observations from either Chandra or XMM-Newton. The sample can be used to investigate the non-linear relation between the UV and X-ray luminosity of quasars, and to build a Hubble diagram up to redshift z~7.5. We selected sources that are neither reddened by dust in the optical/UV nor obscured by gas in the X-rays, and whose X-ray fluxes are free from flux-limit related biases. After checking for any possible systematics, we confirm, in agreement with our previous works, that (i) the X-ray to UV relation provides distance estimates matching those from supernovae up to z~1.5, and (ii) its slope shows no redshift evolution up to z~5. We provide a full description of the methodology for testing cosmological models, further supporting a trend whereby the Hubble diagram of quasars is well reproduced by the standard flat LambdaCDM model up to z~1.5-2, but strong deviations emerge at higher redshifts. Since we have minimized all non-negligible systematic effects, and proven the stability of the Lx-Lo relation at high redshifts, we conclude that an evolution of the expansion rate of the Universe should be considered as a possible explanation for the observed deviation, rather than some systematic (redshift-dependent) effect associated with high-redshift quasars.
- ID:
- ivo://CDS.VizieR/J/AJ/123/578
- Title:
- Quasars in the Coma cluster
- Short Name:
- J/AJ/123/578
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- This is the second paper of the series about our Multiwavelength Quasar Survey. We present the observational results for the X-ray candidates in the field of the Coma Cluster. Nine new X-ray active galactic nuclei are discovered.
- ID:
- ivo://CDS.VizieR/J/AJ/125/1537
- Title:
- QUIRC Chandra sources in OMC 2/3
- Short Name:
- J/AJ/125/1537
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We conducted deep near-infrared (NIR) imaging observations of Orion molecular clouds 2 and 3 using the Quick Infrared Camera on the 88 inch (2.2m) telescope of the University of Hawaii. Our purposes were (1) to generate a comprehensive NIR source catalog of these star-forming clouds and (2) to identify the NIR counterpart of the Chandra X-ray sources that have no counterpart in the Two Micron All Sky Survey (2MASS) catalog. Our J-, H-, and K-band observations are ~2mag deeper than those of 2MASS and match the current Chandra observation well. We detected 1448 NIR sources, for which we derived the position, the J-, H-, and K-band magnitude, and the 2MASS counterpart. Using this catalog, we identified the NIR counterpart for ~42% of the 2MASS unidentified Chandra sources. The nature of these Chandra sources are discussed using their NIR colors and spatial distributions, and a dozen protostar and brown dwarf candidates are identified.
