- 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.
Number of results to display per page
Search Results
- 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50 previously unpublished) at z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.
- 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.
- 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.
645. 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.
- ID:
- ivo://CDS.VizieR/J/ApJ/804/L15
- Title:
- SDSS-DR7 broad-line QSOs
- Short Name:
- J/ApJ/804/L15
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The diverse properties of broad-line quasars appear to follow a well-defined main sequence along which the optical FeII strength increases. It has been suggested that this sequence is mainly driven by the Eddington ratio (L/L_Edd_) of the black hole (BH) accretion. Shen & Ho (2014Natur.513..210S) demonstrated with quasar clustering analysis that the average BH mass decreases with increasing FeII strength when quasar luminosity is fixed, consistent with this suggestion. Here we perform an independent test by measuring the stellar velocity dispersion {sigma}_*_ (hence, the BH mass via the M-{sigma}_*_ relation) from decomposed host spectra in low-redshift Sloan Digital Sky Survey quasars. We found that at fixed quasar luminosity, {sigma}_*_ systematically decreases with increasing FeII strength, confirming that the Eddington ratio increases with FeII strength. We also found that at fixed luminosity and FeII strength, there is little dependence of {sigma}_*_ on the broad H{beta} FWHM. These new results reinforce the framework that the Eddington ratio and orientation govern most of the diversity seen in broad-line quasar properties.
- ID:
- ivo://CDS.VizieR/J/MNRAS/450/3893
- Title:
- SDSS DR10 catalogue of candidate quasars
- Short Name:
- J/MNRAS/450/3893
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We discuss whether modern machine learning methods can be used to characterize the physical nature of the large number of objects sampled by the modern multi-band digital surveys. In particular, we applied the MLPQNA (Multi Layer Perceptron with Quasi Newton Algorithm) method to the optical data of the Sloan Digital Sky Survey - Data Release 10, investigating whether photometric data alone suffice to disentangle different classes of objects as they are defined in the SDSS spectroscopic classification. We discuss three groups of classification problems: (i) the simultaneous classification of galaxies, quasars and stars; (ii) the separation of stars from quasars; (iii) the separation of galaxies with normal spectral energy distribution from those with peculiar spectra, such as starburst or starforming galaxies and AGN. While confirming the difficulty of disentangling AGN from normal galaxies on a photometric basis only, MLPQNA proved to be quite effective in the three-class separation. In disentangling quasars from stars and galaxies, our method achieved an overall efficiency of 91.31% and a QSO class purity of ~95%. The resulting catalogue of candidate quasars/AGNs consists of ~3.6 million objects, of which about half a million are also flagged as robust candidates.
- ID:
- ivo://CDS.VizieR/J/MNRAS/477/5625
- Title:
- SDSSDR12 eclipsing damped Lyalpha systems
- Short Name:
- J/MNRAS/477/5625
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present the results of our automatic search for proximate damped Ly{alpha} absorption (PDLA) systems in the quasar spectra from the Sloan Digital Sky Survey Data Release 12. We constrain our search to those PDLAs lying within 1500km/s from the quasar to make sure that the broad DLA absorption trough masks most of the strong Ly{alpha} emission from the broad-line region (BLR) of the quasar. When the Ly{alpha} emission from the BLR is blocked by these so-called eclipsing DLAs, narrow Ly{alpha} emission from the host galaxy could be revealed as a narrow emission line (NEL) in the DLA trough. We define a statistical sample of 399 eclipsing DLAs with logN(HI)>=21.10. We divide our statistical sample into three subsamples based on the strength of the NEL detected in the DLA trough. By studying the stacked spectra of these subsamples, we found that absorptions from high ionization species are stronger in DLAs with stronger NEL in their absorption core. Moreover, absorption from the excited states of species like SIII are also stronger in DLAs with stronger NEL. We also found no correlation between the luminosity of the Ly{alpha} NEL and the quasar luminosity. These observations are consistent with a scenario in which the DLAs with stronger NEL are denser and physically closer to the quasar. We propose that these eclipsing DLAs could be the product of the interaction between infalling and outflowing gas. High-resolution spectroscopic observation would be needed to shed some light on the nature of these eclipsing DLAs.
- ID:
- ivo://CDS.VizieR/J/MNRAS/397/1713
- Title:
- SDSS DR3 flat-spectrum radio quasars
- Short Name:
- J/MNRAS/397/1713
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We constructed a sample of 185 flat-spectrum radio quasars (FSRQs) by cross-correlating Shen et al.'s (2006MNRAS.369.1639S) Sloan Digital Sky Survey Data Release 3 (SDSS DR3) X-ray quasar sample with the Faint Images of the Radio Sky at Twenty Centimeters (FIRST) and Green Bank 6-cm survey (GB6) radio catalogues. From the spectral energy distribution (SED) constructed using multi-band (radio, UV, optical, infrared and X-ray) data, we derived the synchrotron peak frequency and peak luminosity. The black hole mass MBH and the broad-line region (BLR) luminosity (then the bolometric luminosity Lbol) were obtained by measuring the linewidth and strength of broad emission lines from SDSS spectra. We define a subsample of 118 FSRQs for which non-thermal jet emission is thought to dominate over thermal emission from the accretion disc and host galaxy.
- ID:
- ivo://CDS.VizieR/J/AJ/142/122
- Title:
- SDSS DR7 galaxy/QSOs pairs
- Short Name:
- J/AJ/142/122
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The aim of this project is to identify low-redshift host galaxies of quasar absorption-line systems by selecting galaxies that are seen in projection onto quasar sightlines. To this end, we use the Seventh Data Release of the Sloan Digital Sky Survey to construct a parent sample of 97489 galaxy/quasar projections at impact parameters of up to 100 kpc to the foreground galaxy. We then search the quasar spectra for absorption-line systems of CaII and NaI within +/-500km/s1 of the galaxy's velocity. This yields 92 CaII and 16 NaI absorption systems.
