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671. 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.
672. Quasar 3C 345 at 18 cm with RadioAstron
ID:
ivo://CDS.VizieR/J/A+A/648/A82
Title:
Quasar 3C 345 at 18 cm with RadioAstron
Short Name:
J/A+A/648/A82
Date:
23 Mar 2022 16:32:52
Publisher:
CDS
Description:
Supermassive black holes in the centres of radio-loud active galactic nuclei (AGN) can produce collimated relativistic outflows (jets). Magnetic fields are thought to play a key role in the formation and collimation of these jets, but the details are much debated. We study the innermost jet morphology and magnetic field strength in the AGN 3C 345 with an unprecedented resolution using images obtained within the framework of the key science programme on AGN polarisation of the Space VLBI mission RadioAstron. We observed the flat spectrum radio quasar 3C 345 at 1.6GHz on 2016 March 30 with RadioAstron and 18 ground-based radio telescopes in full polarisation mode. Our images, in both total intensity and linear polarisation, reveal a complex jet structure at 300{mu}as as angular resolution, corresponding to a projected linear scale of about 2pc or a few thousand gravitational radii. We identify the synchrotron self-absorbed core at the jet base and find the brightest feature in the jet 1.5 mas downstream of the core. Several polarised components appear in the Space VLBI images that cannot be seen from ground array-only images. Except for the core, the electric vector position angles follow the local jet direction, suggesting a magnetic field perpendicular to the jet. This indicates the presence of plane perpendicular shocks in these regions. Additionally, we infer a minimum brightness temperature at the largest uv-distances of 1.1x10^12^K in the source frame, which is above the inverse Compton limit and an order of magnitude larger than the equipartition value. This indicates locally efficient injection or re-acceleration of particles in the jet to counter the inverse Compton cooling or the geometry of the jet creates significant changes in the Doppler factor, which has to be >11 to explain the high brightness temperatures.
673. Quasar composite made from bright QSOs
ID:
ivo://CDS.VizieR/J/A+A/585/A87
Title:
Quasar composite made from bright QSOs
Short Name:
J/A+A/585/A87
Date:
21 Oct 2021
Publisher:
CDS
Description:
Quasi-stellar object (QSO) spectral templates are important both to QSO physics and for investigations that use QSOs as probes of intervening gas and dust. However, combinations of various QSO samples obtained at different times and with different instruments so as to expand a composite and to cover a wider rest frame wavelength region may create systematic effects, and the contribution from QSO hosts may contaminate the composite. We have constructed a composite spectrum from luminous blue QSOs at 1<z<2.1 selected from the Sloan Digital Sky Survey (SDSS). The observations with X-shooter simultaneously cover ultraviolet (UV) to near-infrared (NIR) light, which ensures that the composite spectrum covers the full rest-frame range from Ly{beta} to 11350{AA} without any significant host contamination. Assuming a power-law continuum for the composite we find a spectral slope of {alpha}{lambda}=1.70+/-0.01, which is steeper than previously found in the literature. We attribute the differences to our broader spectral wavelength coverage, which allows us to effectively avoid fitting any regions that are affected either by strong QSO emissions lines (e.g., Balmer lines and complex [FeII] blends) or by intrinsic host galaxy emission. Finally, we demonstrate the application of the QSO composite spectrum for evaluating the reddening in other QSOs.
674. 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.
675. 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.
676. Quasar-galaxy associations
ID:
ivo://CDS.VizieR/J/AZh/78/675
Title:
Quasar-galaxy associations
Short Name:
J/AZh/78/675
Date:
21 Oct 2021
Publisher:
CDS
Description:
A new catalog of 8382 close quasar-galaxy pairs is presented. The catalog was composed using published catalogued quasars and active galactic nuclei containing 11358 objects, as well as the LEDA catalog of galaxies, which contains on the order of 100000 objects.
677. Quasar luminosity function
ID:
ivo://CDS.VizieR/J/MNRAS/260/202
Title:
Quasar luminosity function
Short Name:
J/MNRAS/260/202
Date:
21 Oct 2021
Publisher:
CDS
Description:
A sample of quasars is selected from a 10-yr sequence of 30 UK Schmidt plates. Luminosity functions are derived in several redshift intervals, which in each case show a featureless power-law rise towards low luminosities. There is no sigh of the 'break' found in the recent UVX sample of Boyle, Shanks & Peterson. It is suggested that reasons for the disagreement are connected with biases in the selection of the UVX sample. The question of the nature of quasar evolution appears to be still unresolved.
678. 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.
679. Quasar pairs spectroscopy
ID:
ivo://CDS.VizieR/J/ApJ/762/L19
Title:
Quasar pairs spectroscopy
Short Name:
J/ApJ/762/L19
Date:
21 Oct 2021
Publisher:
CDS
Description:
The hosts of luminous z~2 quasars evolve into today's massive elliptical galaxies. Current theories predict that the circumgalactic medium (CGM) of these massive, dark matter halos (M_DM_~10^12.5^M_{sun}_) should be dominated by a T~10^7^K virialized plasma. We test this hypothesis with observations of 74 close-projected quasar pairs, using spectra of the background QSO to characterize the CGM of the foreground one. Surprisingly, our measurements reveal a cool (T~10^4^K), massive (M_CGM_>10^10^M_{sun}_), and metal-enriched (Z>~0.1Z_{sun}_) medium extending to at least the expected virial radius (r_vir_=160kpc). Furthermore, we conservatively estimate that the quasar CGM has a 64^+6^_-7_% covering fraction of optically thick gas (N_HI_>10^17.2^/cm^2^) within r_vir_; this covering factor is twice that of the contemporaneous Lyman break galaxy population. This unexpected reservoir of cool gas is rarely detected "down-the-barrel" to quasars, and hence it is likely that our background sight lines intercept gas that is shadowed from the quasar ionizing radiation by the same obscuring medium often invoked in models of active galactic nucleus unification. Because the high-z halos inhabited by quasars predate modern groups and clusters, these observations are also relevant to the formation and enrichment history of the intragroup/intracluster medium.
680. Quasar polarization
ID:
ivo://CDS.VizieR/J/A+A/340/371
Title:
Quasar polarization
Short Name:
J/A+A/340/371
Date:
21 Oct 2021
Publisher:
CDS
Description:
Table 2 contains optical (V) polarimetric measurements for 42 optically selected QSOs including 29 broad absorption line QSOs. Table 3 contains a series of spectral indices characterizing the broad absorption line QSOs.