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1471. QSO candidates selection in VO era
ID:
ivo://CDS.VizieR/J/MNRAS/396/223
Title:
QSO candidates selection in VO era
Short Name:
J/MNRAS/396/223
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a method for the photometric selection of candidate quasars in multiband surveys. The method makes use of a priori knowledge derived from a subsample of spectroscopic confirmed quasi-stellar objects (QSOs) to map the parameter space. The disentanglement of QSOs candidates and stars is performed in the colour space through the combined use of two algorithms, the probabilistic principal surfaces and the negative entropy clustering, which are for the first time used in an astronomical context. Both methods have been implemented in the voneural package on the Astrogrid Virtual Observatory platform. Even though they belong to the class of the unsupervised clustering tools, the performances of the method are optimized by using the available sample of confirmed quasars and it is therefore possible to learn from any improvement in the available 'base of knowledge'. The method has been applied and tested on both optical and optical plus near-infrared data extracted from the visible Sloan Digital Sky Survey (SDSS) and infrared United Kingdom Infrared Deep Sky Survey-Large Area Survey public data bases. In all cases, the experiments lead to high values of both efficiency and completeness, comparable if not better than the methods already known in the literature. A catalogue of optical candidate QSOs extracted from the SDSS Data Release 7 Legacy photometric data set has been produced.
1472. QSO luminosity function at z~4
ID:
ivo://CDS.VizieR/J/ApJ/710/1498
Title:
QSO luminosity function at z~4
Short Name:
J/ApJ/710/1498
Date:
21 Oct 2021
Publisher:
CDS
Description:
The evolution of the quasar luminosity function (QLF) is one of the basic cosmological measures providing insight into structure formation and mass assembly in the universe. We have conducted a spectroscopic survey to find faint quasars (-26.0<M_1450_<-22.0) at redshifts z=3.8-5.2 in order to measure the faint end of the QLF at these early times. Using available optical imaging data from portions of the NOAO Deep Wide-Field Survey and the Deep Lens Survey, we have color-selected quasar candidates in a total area of 3.76deg^2^. Thirty candidates have R<=23mag. We conducted spectroscopic follow-up for 28 of our candidates and found 23 QSOs, 21 of which are reported here for the first time, in the 3.74<z<5.06 redshift range.
1473. QSO properties from SDSS-DR7
ID:
ivo://CDS.VizieR/J/ApJS/194/45
Title:
QSO properties from SDSS-DR7
Short Name:
J/ApJS/194/45
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a compilation of properties of the 105783 quasars in the Sloan Digital Sky Survey Data Release 7 (DR7) quasar catalog (Cat. VII/260). In this product, we compile continuum and emission line measurements around the H{alpha}, H{beta}, MgII, and CIV regions, as well as other quantities such as radio properties, and flags indicating broad absorption line quasars, disk emitters, etc. We also compile virial black hole mass estimates based on various calibrations. For the fiducial virial mass estimates we use the Vestergaard & Peterson (VP06; 2006ApJ...641..689V) calibrations for H{beta} and CIV, and our own calibration for MgII which matches the VP06 H{beta} masses on average. We describe the construction of this catalog and discuss its limitations.
1474. QSOs and RR Lyrae in Pan-STARRS1 3{pi} Data
ID:
ivo://CDS.VizieR/J/ApJ/817/73
Title:
QSOs and RR Lyrae in Pan-STARRS1 3{pi} Data
Short Name:
J/ApJ/817/73
Date:
21 Oct 2021
Publisher:
CDS
Description:
In area and depth, the Pan-STARRS1 (PS1) 3{pi} survey is unique among many-epoch, multi-band surveys and has enormous potential for the all-sky identification of variable sources. PS1 has observed the sky typically seven times in each of its five bands (grizy) over 3.5 years, but unlike SDSS, not simultaneously across the bands. We developed a new approach for quantifying statistical properties of non-simultaneous, sparse, multi-color light curves through light curve structure functions, effectively turning PS1 into a {sim}35-epoch survey. We use this approach to estimate variability amplitudes and timescales for point sources brighter than r_P1_=21.5 mag in the survey. On this basis we provide a catalog of all likely variable point sources and likely QSOs in PS1.
1475. QSOs SED shapes from optical to NIR
ID:
ivo://CDS.VizieR/J/MNRAS/434/3104
Title:
QSOs SED shapes from optical to NIR
Short Name:
J/MNRAS/434/3104
Date:
21 Oct 2021
Publisher:
CDS
Description:
We define a quasar-galaxy mixing diagram using the slopes of their spectral energy distributions (SEDs) from 1{mu}m to 3000{AA} and from 1 to 3{mu}m in the rest frame. The mixing diagram can easily distinguish among quasar-dominated, galaxy-dominated and reddening-dominated SED shapes. By studying the position of the 413 XMM-selected type 1 AGN in the wide-field 'Cosmic Evolution Survey' in the mixing diagram, we find that a combination of the Elvis et al. (2012ApJ...759....6E, Cat. J/ApJ/759/6) mean quasar SED with various contributions from galaxy emission and some dust reddening is remarkably effective in describing the SED shape from 0.3 to 3{mu}m for large ranges of redshift, luminosity, black hole mass and Eddington ratio of type 1 AGN. In particular, the location in the mixing diagram of the highest luminosity AGN is very close (within 1{sigma}) to that of the Elvis et al. (2012ApJ...759....6E, Cat. J/ApJ/759/6) SED template. The mixing diagram can also be used to estimate the host galaxy fraction and reddening in quasar. We also show examples of some outliers which might be AGN in different evolutionary stages compared to the majority of AGN in the quasar-host galaxy co-evolution cycle.
1476. Quasar candidates selected from the SDSS
ID:
ivo://CDS.VizieR/J/AJ/137/3884
Title:
Quasar candidates selected from the SDSS
Short Name:
J/AJ/137/3884
Date:
21 Oct 2021
Publisher:
CDS
Description:
We explore the multidimensional, multiwavelength selection of quasars from mid-infrared (MIR) plus optical data, specifically from Spitzer-Infrared Array Camera (IRAC) and the Sloan Digital Sky Survey (SDSS). Traditionally, quasar selection relies on cuts in two-dimensional color space despite the fact that most modern surveys (optical and IR) are done in more than three bandpasses. In this paper, we apply modern statistical techniques to combined Spitzer MIR and SDSS optical data, allowing up to eight-dimensional (8-D) color selection of quasars. Using a Bayesian selection method, we catalog 5546 quasar candidates to an 8.0{mu}m depth of 56{mu}Jy over an area of ~24{deg}^2^. Roughly 70% of these candidates are not identified by applying the same Bayesian algorithm to 4-color SDSS optical data alone. The 8-D optical+MIR selection on this data set recovers 97.7% of known type 1 quasars in this area and greatly improves the effectiveness of identifying 3.5<z<5 quasars which are challenging to identify (without considerable contamination) using MIR data alone.
1477. Quasar evolution
ID:
ivo://CDS.VizieR/J/ApJ/269/352
Title:
Quasar evolution
Short Name:
J/ApJ/269/352
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the Bright Quasar Survey (BQS) consisting of 114 objects to an average limiting magnitude B=16.16 over an area of 10714{deg}^2^. There are 92 quasars with M_B_<-23 in the sample. We use the BQS and complete samples from published surveys to derive models of the statistical evolution of quasars. The increase of space density with redshift depends strongly on absolute luminosity, being close to zero for low-luminosity quasars. Detailed predictions are given for the distribution of redshifts and magnitudes and for the total counts based on the evolution models.
1478. Quasar from SDSS and UKIDSS
ID:
ivo://CDS.VizieR/J/MNRAS/406/1583
Title:
Quasar from SDSS and UKIDSS
Short Name:
J/MNRAS/406/1583
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a sample of 8498 quasars with both Sloan Digital Sky Survey (SDSS) ugriz optical and United Kingdom Infrared Telescope (UKIRT) Infrared Deep Sky Survey (UKIDSS) YJHK near-infrared (near-IR) photometric data. With this sample, we obtain the median colour-z relations based on 7400 quasars with magnitude uncertainties less than 0.1mag in all bands. By analysing the quasar colours, we propose an empirical criterion in the Y-K versus g-z colour-colour diagram to separate stars and quasars with redshift z<4, and two other criteria for selecting high-redshift quasars. Using the SDSS-UKIDSS colour-z relations, we estimate the photometric redshifts of 8498 SDSS-UKIDSS quasars, and find that 85.0 per cent of them are consistent with the spectroscopic redshifts within |{Delta}z|<0.2, which leads to a significant increase of the photometric redshift accuracy from that based on the SDSS colour-z relations only. As two tests, we compare our colour-selection criterion with a small UKIDSS/EDR quasar/star sample and a sample of 4671 variable sources in the SDSS Stripe 82 region with both SDSS and UKIDSS data. We find that they can be clearly divided into two classes (quasars and stars) by our criterion in the Y-K versus g-z plot.
1479. Quasar luminosity function from SDSS-DR3
ID:
ivo://CDS.VizieR/J/AJ/131/2766
Title:
Quasar luminosity function from SDSS-DR3
Short Name:
J/AJ/131/2766
Date:
21 Oct 2021
Publisher:
CDS
Description:
We determine the number counts and z=0-5 luminosity function for a well-defined, homogeneous sample of quasars from the Sloan Digital Sky Survey (SDSS). We conservatively define the most uniform statistical sample possible, consisting of 15343 quasars within an effective area of 1622{deg}^2^ that was derived from a parent sample of 46420 spectroscopically confirmed broad-line quasars in the 5282{deg}^2^ of imaging data from SDSS Data Release 3. The sample extends from i=15 to 19.1 at z<~3 and to i=20.2 for z>~3.
1480. Quasars from 7C survey
ID:
ivo://CDS.VizieR/J/MNRAS/307/293
Title:
Quasars from 7C survey
Short Name:
J/MNRAS/307/293
Date:
21 Oct 2021
Publisher:
CDS
Description:
We describe the selection of candidate radio-loud quasars obtained by cross-matching radio source positions from the low-frequency (151-MHz) 7C survey with optical positions from five pairs of EO POSS-1 plates scanned with the Cambridge Automatic Plate-measuring Machine (APM). The sky region studied is centred at RA=10h28m, DE=+41{deg} and covers ~0.057sr. We present VLA observations of the quasar candidates, and tabulate various properties derived from the radio maps. We discuss the selection criteria of the resulting '7CQ' sample of radio-loud quasars. The 70 confirmed quasars, and some fraction of the 36 unconfirmed candidates, constitute a filtered sample with the following selection criteria: 151-MHz flux density S_151_>100mJy; POSS-I E-plate magnitude E~R<20; POSS-I colour (O-E)<1.8; the effective area of the survey drops significantly below S_151_~200mJy. We argue that the colour criterion excludes few if any quasars, but note, on the basis of recent work by Willott et al. (1998MNRAS.300..625W), that the E magnitude limit probably excludes more than 50 per cent of the radio-loud quasars.

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