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781. SDSS 2175{AA} extinction bump candidates
ID:
ivo://CDS.VizieR/J/ApJ/732/110
Title:
SDSS 2175{AA} extinction bump candidates
Short Name:
J/ApJ/732/110
Date:
21 Oct 2021
Publisher:
CDS
Description:
We report detections of 39 2175{AA} dust extinction bump candidates associated with strong MgII absorption lines at z~1-1.8 on quasar spectra in Sloan Digital Sky Survey (SDSS) DR3. These strong MgII absorption line systems are detected among 2951 strong MgII absorbers with a rest equivalent width W_r_{lambda}2796>1.0{AA} at 1.0<z<1.86, which is part of a full sample of 7421 strong MgII absorbers compiled by Prochter et al. (2006, Cat. J/ApJ/639/766). The redshift range of the absorbers is chosen to allow the 2175{AA} extinction features to be completely covered within the SDSS spectrograph operation wavelength range. An upper limit of the background quasar emission redshift at z=2.1 is set to prevent the Ly{alpha} forest lines from contaminating the sensitive spectral region for the 2175{AA} bump measurements. A total of 12 absorbers are detected with 2175{AA} bumps at a 5{sigma} level of statistical significance, 10 are detected at a 4{sigma} level, and 17 are detected at a 3{sigma} level. Most of the candidate bumps in this work are similar to the relatively weak 2175{AA} bumps observed in the Large Magellanic Cloud LMC2 supershell rather than the strong ones observed in the Milky Way.
782. SDSS and DES long-term extreme variability QSOs
ID:
ivo://CDS.VizieR/J/ApJ/854/160
Title:
SDSS and DES long-term extreme variability QSOs
Short Name:
J/ApJ/854/160
Date:
21 Oct 2021
Publisher:
CDS
Description:
We perform a systematic search for long-term extreme variability quasars (EVQs) in the overlapping Sloan Digital Sky Survey and 3 Year Dark Energy Survey imaging, which provide light curves spanning more than 15 years. We identified ~1000 EVQs with a maximum change in g-band magnitude of more than 1 mag over this period, about 10% of all quasars searched. The EVQs have L_bol_~10^45^-10^47^erg/s and L/L_Edd_~0.01-1. Accounting for selection effects, we estimate an intrinsic EVQ fraction of ~30%-50% among all g<~22 quasars over a baseline of ~15yr. We performed detailed multi-wavelength, spectral, and variability analyses for the EVQs and compared them to their parent quasar sample. We found that EVQs are distinct from a control sample of quasars matched in redshift and optical luminosity: (1) their UV broad emission lines have larger equivalent widths; (2) their Eddington ratios are systematically lower; and (3) they are more variable on all timescales. The intrinsic difference in quasar properties for EVQs suggests that internal processes associated with accretion are the main driver for the observed extreme long-term variability. However, despite their different properties, EVQs seem to be in the tail of a continuous distribution of quasar properties, rather than standing out as a distinct population. We speculate that EVQs are normal quasars accreting at relatively low rates, where the accretion flow is more likely to experience instabilities that drive the changes in flux by a factor of a few on multi-year timescales.
783. SDSS binary quasars at high redshift. I.
ID:
ivo://CDS.VizieR/J/ApJ/719/1672
Title:
SDSS binary quasars at high redshift. I.
Short Name:
J/ApJ/719/1672
Date:
21 Oct 2021
Publisher:
CDS
Description:
The clustering of quasars on small scales yields fundamental constraints on models of quasar evolution and the buildup of supermassive black holes. This paper describes the first systematic survey to discover high-redshift binary quasars. Using color-selection and photometric redshift techniques, we searched 8142deg^2^ of Sloan Digital Sky Survey imaging data for binary quasar candidates, and confirmed them with follow-up spectroscopy. Our sample of 27 high-redshift binaries (24 of them new discoveries) at redshifts 2.9<z<4.3 with proper transverse separations 10kpc<R_T_<650kpc increases the number of such objects known by an order of magnitude. Eight members of this sample are very close pairs with R_T_<100kpc, and of these close systems four are at z>3.5. The completeness and efficiency of our well-defined selection algorithm are quantified using simulated photometry and we find that our sample is ~50% complete.
784. SDSS/BOSS/TDSS CIV BAL quasars
ID:
ivo://CDS.VizieR/J/ApJ/824/130
Title:
SDSS/BOSS/TDSS CIV BAL quasars
Short Name:
J/ApJ/824/130
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present results from the largest systematic investigation of broad absorption line (BAL) acceleration to date. We use spectra of 140 quasars from three Sloan Digital Sky Survey programs to search for global velocity offsets in BALs over timescales of ~2.5-5.5 years in the quasar rest frame. We carefully select acceleration candidates by requiring monolithic velocity shifts over the entire BAL trough, avoiding BALs with velocity shifts that might be caused by profile variability. The CIV BALs of two quasars show velocity shifts consistent with the expected signatures of BAL acceleration, and the BAL of one quasar shows a velocity-shift signature of deceleration. In our two acceleration candidates, we see evidence that the magnitude of the acceleration is not constant over time; the magnitudes of the change in acceleration for both acceleration candidates are difficult to produce with a standard disk-wind model or via geometric projection effects. We measure upper limits to acceleration and deceleration for 76 additional BAL troughs and find that the majority of BALs are stable to within about 3% of their mean velocities. The lack of widespread acceleration/deceleration could indicate that the gas producing most BALs is located at large radii from the central black hole and/or is not currently strongly interacting with ambient material within the host galaxy along our line of sight.
785. SDSS candidate type II quasars
ID:
ivo://CDS.VizieR/J/AJ/126/2125
Title:
SDSS candidate type II quasars
Short Name:
J/AJ/126/2125
Date:
21 Oct 2021
Publisher:
CDS
Description:
Type II quasars are the long-sought luminous analogs of type 2 (narrow emission line) Seyfert galaxies, suggested by unification models of active galactic nuclei (AGNs) and postulated to account for an appreciable fraction of the cosmic hard X-ray background. We present a sample of 291 type II AGNs at redshifts 0.3<z<0.83 from the spectroscopic data of the Sloan Digital Sky Survey. These objects have narrow (FWHM<2000km/s), high equivalent width emission lines with high-ionization line ratios. We describe the selection procedure and discuss the optical properties of the sample. About 50% of the objects have [O III] {lambda}5008 line luminosities in the range 3x10^8^-10^10^L_{sun}_, comparable to those of luminous (-27<M_B_<-23) quasars; this, along with other evidence, suggests that the objects in the luminous subsample are type II quasars.
786. SDSS candidate type II quasars. II
ID:
ivo://CDS.VizieR/J/AJ/128/1002
Title:
SDSS candidate type II quasars. II
Short Name:
J/AJ/128/1002
Date:
21 Oct 2021
Publisher:
CDS
Description:
Type II quasars are luminous active galactic nuclei (AGNs) whose central engines and broad-line regions are obscured by intervening material; such objects only recently have been discovered in appreciable numbers. We study the multiwavelength properties of 291 type II AGN candidates (0.3<z<0.8) selected on the basis of their optical emission-line properties from the spectroscopic database of the Sloan Digital Sky Survey (Cat. <J/AJ/126/2579>). This sample includes about 150 objects luminous enough to be classified as type II quasars. We matched the sample to the FIRST (20cm, Cat.<VIII/71>), IRAS (12-100{mu}m, Cat. <II/125>), 2MASS (JHK_s_, Cat. <II/246>), and RASS (0.1-2.4keV, Cat. <IX/29>) surveys. Roughly 10% of optically selected type II AGN candidates are radio-loud, comparable to the AGN population as a whole. About 40 objects are detected by IRAS at 60 and/or 100{mu}m, and the inferred mid/far-IR luminosities lie in the range L=10^45^-3x10^46^ergs/s. Average IR-to-[OIII]{lambda}5007 ratios of objects in our sample are consistent with those of other AGNs. Objects from our sample are 10 times less likely to have soft X-ray counterparts in RASS than type I AGNs with the same redshifts and [OIII]{lambda}5007 luminosities. The few type II AGN candidates from our sample that are detected by RASS have harder X-ray spectra than those of type I AGNs. The multiwavelength properties of the type II AGN candidates from our sample are consistent with their interpretation as powerful obscured AGNs.
787. SDSS damped Ly{alpha} survey: DR1
ID:
ivo://CDS.VizieR/J/PASP/116/622
Title:
SDSS damped Ly{alpha} survey: DR1
Short Name:
J/PASP/116/622
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the results from an automated search for damped Ly{alpha} (DLA) systems in the quasar spectra of Data Release 1 from the Sloan Digital Sky Survey (SDSS-DR1). At z~2.5, this homogeneous data set has greater statistical significance than the previous two decades of research. We derive a statistical sample of 71 DLA systems (>50 previously unpublished) at z>2.1 and measure HI column densities directly from the SDSS spectra.
788. SDSS DLA and absorber quasar samples
ID:
ivo://CDS.VizieR/J/MNRAS/455/1043
Title:
SDSS DLA and absorber quasar samples
Short Name:
J/MNRAS/455/1043
Date:
21 Oct 2021
Publisher:
CDS
Description:
The dust content of damped Lyman {alpha} systems (DLAs) is an important observable for understanding their origin and the neutral gas reservoirs of galaxies. While the average colour excess of DLAs, E(B-V), is known to be <~15-millimagnitude (mmag), both detections and non-detections with ~2mmag precision have been reported. Here we find 3.2{sigma} statistical evidence for DLA dust-reddening of 774 Sloan Digital Sky Survey (SDSS) quasars by comparing their fitted spectral slopes to those of ~7000 control quasars. The corresponding E(B-V) is 3.0+/-1.0mmag, assuming a Small Magellanic Cloud (SMC) dust extinction law, and it correlates strongly (3.5{sigma}) with the metal content, characterized by the SiII {lambda}1526 absorption-line equivalent width, providing additional confidence that the detection is due to dust in the DLAs. Evolution of E(B-V) over the redshift range 2.1<z<4.0 is limited to <2.5mmag per unit redshift (1{sigma}), consistent with the known, mild DLA metallicity evolution. There is also no apparent relationship with neutral hydrogen column density, N_HI_, though the data are consistent with a mean E(B-V)/N_HI_=(3.5+/-1.0)*10^-24^mag*cm^2^, approximately the ratio expected from the SMC scaled to the lower metallicities typical of DLAs. We implement the SDSS selection algorithm in a portable code to assess the potential for systematic, redshift-dependent biases stemming from its magnitude and colour-selection criteria. The effect on the mean E(B-V) is negligible (<5 per cent) over the entire redshift range of interest. Given the broad potential usefulness of this implementation, we make it publicly available.
789. SDSS DR5 BALQSO catalog
ID:
ivo://CDS.VizieR/J/MNRAS/399/2231
Title:
SDSS DR5 BALQSO catalog
Short Name:
J/MNRAS/399/2231
Date:
21 Oct 2021
Publisher:
CDS
Description:
We apply a recently developed method for classifying broad absorption line quasars (BALQSOs) to the latest QSO catalogue constructed from Data Release 5 of the Sloan Digital Sky Survey. Our new hybrid classification method combines the power of simple metrics, supervised neural networks and visual inspection. The resulting BALQSO catalogue is both more complete and more robust than all previous BALQSO catalogues, containing 3552 sources selected from a parent sample of 28421 QSOs in the redshift range 1.7<z<4.2. This equates to a raw BAL QSO fraction of 12.5%. In the process of constructing a robust catalogue we shed light on the main problems encountered when dealing with BALQSO classification, in particular when the astronomical objects in question do not yet have a formal definition as is the case for BALQSOs. This introduces some subjectivity on what is meant by BALQSO, and because of this we also provide meta-data of our catalogue, comprising our whole parent sample which can be used to quickly isolate and explore various sub-samples.
790. SDSS DR2 BAL QSOs
ID:
ivo://CDS.VizieR/J/ApJ/665/990
Title:
SDSS DR2 BAL QSOs
Short Name:
J/ApJ/665/990
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have investigated a sample of 5088 quasars from the SDSS DR2 in order to determine how the frequency and properties of BALs depend on black hole mass, bolometric luminosity, Eddington fraction (L/L_Edd_), and spectral slope. We focus only on high-ionization BALs and find a number of significant results. While quasars accreting near the Eddington limit are more likely to show BALs than lower L/LEdd systems, BALs are present in quasars accreting at only a few percent Eddington. We find a stronger effect with bolometric luminosity, such that the most luminous quasars are more likely to show BALs. There is an additional effect, previously known, that BAL quasars are redder on average than unabsorbed quasars. The strongest effects involving the quasar physical properties and BAL properties are related to terminal outflow velocity. Maximum observed outflow velocities increase with both the bolometric luminosity and the blueness of the spectral slope, suggesting that the ultraviolet luminosity to a great extent determines the acceleration. These results support the idea of outflow acceleration via ultraviolet line scattering.

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