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371. Low-redshift quasars in SDSS Stripe 82
ID:
ivo://CDS.VizieR/J/MNRAS/440/476
Title:
Low-redshift quasars in SDSS Stripe 82
Short Name:
J/MNRAS/440/476
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a photometrical and morphological study of the properties of low-redshift (z<0.5) quasars based on a large and homogeneous data set of objects derived from the Sloan Digital Sky Survey Data Release 7. This study over number by a factor of ~5 any other previous study of quasi-stellar object (QSO) host galaxies at low redshift undertaken either on ground or on space surveys. We used ~400 quasars that were imaged in the SDSS Stripe 82 that is up to 2mag deeper than standard Sloan images. For these quasars we undertake a study of the host galaxies and of their environments. In this paper we report the results for the quasar hosts. We are able to detect the host galaxy for more than 3/4 of the whole data set and characterize the properties of their hosts. We found that QSO hosts are dominated by luminous galaxies of absolute magnitude M*-3<M(R)<M*. For the unresolved objects we computed an upper limit to the host luminosity. For each well-resolved quasar we are also able to characterize the morphology of the host galaxy that turn out to be more complex than what found in previous studies. QSOs are hosted in a variety of galaxies from pure ellipticals to complex/composite morphologies that combine spheroids, disc, lens and halo. The black hole (BH) mass of the quasar, estimated from the spectral properties of the nuclei, is poorly correlated with the total luminosity of the host galaxy. However, taking into account only the bulge component we found a significant correlation between the BH mass and the bulge luminosity of the host.
372. Low-z BQS Quasars
ID:
ivo://CDS.VizieR/J/MNRAS/263/425
Title:
Low-z BQS Quasars
Short Name:
J/MNRAS/263/425
Date:
21 Oct 2021
Publisher:
CDS
Description:
(no description available)
373. LQRF: Large Quasar Reference Frame
ID:
ivo://CDS.VizieR/I/313
Title:
LQRF: Large Quasar Reference Frame
Short Name:
I/313
Date:
21 Oct 2021
Publisher:
CDS
Description:
The LQRF (Large Quasar Reference Frame) was built with the care of avoiding wrong matches of its constituents quasars, of homogenizing the astrometry from the different catalogs and lists from which the constituent quasars are gathered, and of attaining the milli-arcsec global alignment to the ICRF (International Celestial Reference Frame), as well as typical individual source position accuracies even to better than 100 milli-arcsec. Starting from the updated and presumably complete LQAC (Large Quasar Astrometric Catalog) list of QSOs, initial optical positions for those quasars are found in the USNO B1.0 and GSC2.3 catalogs, and from the SDSS Data Release 5. The initial positions are next placed onto UCAC2 based reference frames, following by an alignment to the ICRF, as well as of the most precise sources from the VLBA calibrator list and from the VLA calibrator list - when reliable optical counterparts exist. Finally the LQRF axes are inspected through spherical harmonics, contemplating right ascension, declination and magnitude terms.
374. Luminous dust-poor SDSS QSOs at z<4.5
ID:
ivo://CDS.VizieR/J/ApJ/779/104
Title:
Luminous dust-poor SDSS QSOs at z<4.5
Short Name:
J/ApJ/779/104
Date:
21 Oct 2021
Publisher:
CDS
Description:
We identify and characterize a population of luminous, dust-poor quasars at 0<z<5 that is photometrically similar to objects previously found at z>6. This class of active galactic nuclei is known to show little IR emission from dusty structure, but it is poorly understood in terms of number evolution and dependence on physical quantities. To better understand the properties of these quasars, we compile a rest-frame UV to IR library of 41000 optically selected type 1 quasars with L_bol_>10^45.7^erg/s. After fitting the broadband spectral energy distributions (SEDs) with accretion disk and dust components, we find 0.6% of our sample to be hot dust-poor, with rest-frame 2.3{mu}m to 0.51{mu}m flux density ratios of -0.5dex or less. The dust-poor SEDs are blue in the UV-optical and weak in the mid-IR, such that their accretion disks are less obscured and the hot dust emission traces that of warm dust down to the dust-poor regime. At a given bolometric luminosity, dust-poor quasars are lower in black hole mass and higher in Eddington ratio than general luminous quasars, suggesting that they are in a rapidly growing evolutionary state in which the dust-poor phase appears as a short or rare phenomenon. The dust-poor fraction increases with redshift, and possible implications for their evolution are discussed.
375. Luminous K-band selected QSOs from UKIDSS
ID:
ivo://CDS.VizieR/J/MNRAS/386/1605
Title:
Luminous K-band selected QSOs from UKIDSS
Short Name:
J/MNRAS/386/1605
Date:
21 Oct 2021
Publisher:
CDS
Description:
The largest K-band flux-limited sample of luminous quasars to date has been constructed from the UKIRT (UK Infrared Telescope) Infrared Deep Sky Survey (UKIDSS) Large Area Survey Early Data Release, covering an effective area of 12.8deg^2^. Exploiting the K-band excess (KX) of all quasars with respect to foreground stars, including quasars experiencing dust reddening and objects with non-standard spectral energy distributions (SEDs), a list of targets suitable for spectroscopic follow-up observations with the AAOmega multi-object spectrograph is constructed, resulting in more than 200 confirmed active galactic nuclei (AGN). KX selection successfully identifies as quasar candidates objects that are excluded from the Sloan Digital Sky Survey (SDSS) quasar selection algorithm due to their colours being consistent with the stellar locus in optical colour space (with the space density of the excluded objects agreeing well with results from existing completeness analyses). Nearly half of the KX-selected quasars with K<=17.0 at z<3 are too faint in the i band to have been targeted by the SDSS quasar selection algorithm, revealing a large population of quasars with red i-K colours.
376. Luminous of high-z QSOs with SDSS and WISE. II
ID:
ivo://CDS.VizieR/J/ApJ/829/33
Title:
Luminous of high-z QSOs with SDSS and WISE. II
Short Name:
J/ApJ/829/33
Date:
21 Oct 2021
Publisher:
CDS
Description:
This is the second paper in a series on a new luminous z~5 quasar survey using optical and near-infrared colors. Here we present a new determination of the bright end of the quasar luminosity function (QLF) at z~5. Combining our 45 new quasars with previously known quasars that satisfy our selections, we construct the largest uniform luminous z~5 quasar sample to date, with 99 quasars in the range of 4.7<=z<5.4 and -29<M_1450_<=-26.8, within the Sloan Digital Sky Survey (SDSS) footprint. We use a modified 1/V_a_ method including flux limit correction to derive a binned QLF, and we model the parametric QLF using maximum likelihood estimation. With the faint-end slope of the QLF fixed as {alpha}=-2.03 from previous deeper samples, the best fit of our QLF gives a flatter bright end slope {beta}=-3.58+/-0.24 and a fainter break magnitude M_1450_^*^=-26.98+/-0.23 than previous studies at similar redshift. Combined with previous work at lower and higher redshifts, our result is consistent with a luminosity evolution and density evolution model. Using the best-fit QLF, the contribution of quasars to the ionizing background at z~5 is found to be 18%-45% with a clumping factor C of 2-5. Our sample suggests an evolution of radio loud fraction with optical luminosity but no obvious evolution with redshift.
377. Luminous radio galaxies & type-2 quasars
ID:
ivo://CDS.VizieR/J/MNRAS/436/997
Title:
Luminous radio galaxies & type-2 quasars
Short Name:
J/MNRAS/436/997
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results of a comparison between the environments of (1) a complete sample of 46 southern 2-Jy radio galaxies at intermediate redshifts (0.05<z<0.7), (2) a complete sample of 20 radio-quiet type-2 quasars (0.3<=z<=0.41), and (3) a control sample of 107 quiescent early-type galaxies at 0.2<=z<0.7 in the Extended Groth Strip. The environments have been quantified using angular clustering amplitudes (Bgq) derived from deep optical imaging data. Based on these comparisons, we discuss the role of the environment in the triggering of powerful radio-loud and radio-quiet quasars. When we compare the Bgq distributions of the type-2 quasars and quiescent early-type galaxies, we find no significant difference between them. This is consistent with the radio-quiet quasar phase being a short-lived but ubiquitous stage in the formation of all massive early-type galaxies. On the other hand, powerful radio galaxies are in denser environments than the quiescent population, and this difference between distributions of Bgq is significant at the 3{sigma} level. This result supports a physical origin of radio loudness, with high-density gas environments favouring the transformation of active galactic nucleus (AGN) power into radio luminosity, or alternatively, affecting the properties of the supermassive black holes themselves. Finally, focusing on the radio-loud sources only, we find that the clustering of weak-line radio galaxies (WLRGs) is higher than the strong-line radio galaxies (SLRGs), constituting a 3{sigma} result. 82 percent of the 2-Jy WLRGs are in clusters, according to our definition (Bgq>~400), versus only 31 percent of the SLRGs.
378. Luminous WISE-selected quasars in SDSS Stripe 82
ID:
ivo://CDS.VizieR/J/ApJ/861/37
Title:
Luminous WISE-selected quasars in SDSS Stripe 82
Short Name:
J/ApJ/861/37
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a spectroscopically complete sample of 147 infrared-color-selected active galactic nuclei (AGNs) down to a 22{mu}m flux limit of 20mJy over the ~270deg^2^ of the Sloan Digital Sky Survey Stripe 82 region. Most of these sources are in the QSO luminosity regime (Lbol>~10^12^L_{sun}_) and are found out to z~3. We classify the AGNs into three types, finding 57 blue, unobscured Type-1 (broad-lined) sources; 69 obscured, Type-2 (narrow-lined) sources; and 21 moderately reddened Type-1 sources (broad-lined and E(B-V)>0.25). We study a subset of this sample in X-rays and analyze their obscuration to find that our spectroscopic classifications are in broad agreement with low, moderate, and large amounts of absorption for Type-1, red Type-1, and Type-2 AGNs, respectively. We also investigate how their X-ray luminosities correlate with other known bolometric luminosity indicators such as [OIII] line luminosity (L[OIII]) and infrared luminosity (L6{mu}m). While the X-ray correlation with L[OIII] is consistent with previous findings, the most infrared-luminous sources appear to deviate from established relations such that they are either underluminous in X-rays or overluminous in the infrared. Finally, we examine the luminosity function evolution of our sample, and by AGN type, in combination with the complementary, infrared-selected, AGN sample of Lacy et al. (2013), spanning over two orders of magnitude in luminosity. We find that the two obscured populations evolve differently, with reddened Type-1 AGNs dominating the obscured AGN fraction (~30%) for L_5{mu}m_>10^45^erg/s, while the fraction of Type-2 AGNs with L_5{mu}m_<10^45^erg/s rises sharply from 40% to 80% of the overall AGN population.
379. Ly{alpha} absorption systems. V.
ID:
ivo://CDS.VizieR/J/ApJ/559/654
Title:
Ly{alpha} absorption systems. V.
Short Name:
J/ApJ/559/654
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results of a program to obtain and analyze HST WFPC2 images and ground-based images of galaxies identified in an imaging and spectroscopic survey of faint galaxies in fields of HST spectroscopic target QSOs. Here we present the additional HST WFPC2 observations of galaxies in 10 QSO fields that were not included in Paper I (Chen et al., 1998, Cat. <J/ApJ/498/77>) and near-infrared imaging observations of galaxies in 15 QSO fields.
380. Ly{alpha} and OVI in galaxies around quasars
ID:
ivo://CDS.VizieR/J/ApJ/740/91
Title:
Ly{alpha} and OVI in galaxies around quasars
Short Name:
J/ApJ/740/91
Date:
21 Oct 2021
Publisher:
CDS
Description:
We analyze the association of galaxies with Ly{alpha} and OVI absorption, the most commonly detected transitions of the low-z intergalactic medium (IGM), in the fields of 14 quasars with z_em_=0.06-0.57. Confirming previous studies, we observe a high covering fraction for Ly{alpha} absorption to impact parameter {rho}=300h^-1^_72_kpc: 33/37 of our L>0.01L* galaxies show Ly{alpha} equivalent width W^Ly{alpha}^>=50 m{AA}. Galaxies of all luminosity L>0.01L* and spectral type are surrounded by a diffuse and ionized circumgalactic medium (CGM), whose baryonic mass is estimated at ~10^10.5^+/-0.3M_{sun}_ for a constant N_H_=10^19^cm^-2^. The virialized halos and extended CGM of present-day galaxies are responsible for most strong Ly{alpha} absorbers (W^Ly{alpha}^>300m{AA}) but cannot reproduce the majority of observed lines in the Ly{alpha} forest. We conclude that the majority of Ly{alpha} absorption with W^Ly{alpha}^=30-300m{AA} occurs in the cosmic web predicted by cosmological simulations and estimate a characteristic width for these filaments of ~400h^-1^_72_kpc. Regarding OVI, we observe a near unity covering fraction to {rho}=200h^-1^_72_kpc for L>0.1L* galaxies and to {rho}=300h^-1^_72_kpc for sub-L* (0.1 L*<L<L*) galaxies. Similar to our Ly{alpha} results, stronger OVI systems (W^1031^>70m{AA}) arise in the virialized halos of L>0.1L* galaxies. Unlike Ly{alpha}, the weaker OVI systems (W^1031^~30m{AA}) arise in the extended CGM of sub-L* galaxies. The majority of OVI gas observed in the low-z IGM is associated with a diffuse medium surrounding individual galaxies with L~0.3L* and rarely originates in the so-called warm-hot IGM (predicted by cosmological simulations.