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661. SDSS-FIRST quasar sample study
ID:
ivo://CDS.VizieR/J/A+A/630/A110
Title:
SDSS-FIRST quasar sample study
Short Name:
J/A+A/630/A110
Date:
21 Oct 2021
Publisher:
CDS
Description:
When can an active galactic nucleus (AGN) be considered radio-loud? Following the established view of the AGNs inner workings, an AGN is radio-loud if associated with relativistic ejections emitting a radio synchrotron spectrum (i.e., it is a "jetted" AGN). In this paper we exploit the AGN main sequence that offers a powerful tool to contextualize radio properties. If large samples of optically-selected quasars are considered, AGNs are identified as radio-loud if their Kellermann's radio loudness ratio R_K_>10. Our aims are to characterize the optical properties of different classes based on radioloudness within the main sequence and to test whether the condition R_K_>10 is sufficient for the identification of RL AGNs, since the origin of relatively strong radio emission may not be necessarily due to relativistic ejection. A sample of 355 quasars was selected by cross-correlating the FIRST survey with the SDSS DR14 quasar catalog. We classified the optical spectra according to their spectral types along the main sequence of quasars. For each spectral type, we distinguished compact and extended morphology (providing a FIRST-based atlas of radio maps in the latter case), and three classes of radio-loudness: detected (specific flux ratio in the g band and at 1.4GHz, R_K'_<10), intermediate (10R_K'_<70), and radio loud (R_K'_>=70). The analysis revealed systematic differences between radio-detected (i.e., radio-quiet), radio-intermediate, and radio-loud in each spectral type along the main sequence. We show that spectral bins that contain the extreme Population A sources have radio power compatible with emission by mechanisms ultimately due to star formation processes. Radio-loud sources of Population B are characteristically jetted. Their broad H{beta} profiles can be interpreted as due to a binary broad-line region. We suggest that RL Population B sources should be preferential targets for the search of black hole binaries, and present a sample of binary black hole AGN candidates. The validity of the Kellermann's criterion may be dependent on the source location along the quasar main sequence. The consideration of the MS trends allowed to distinguish between sources whose radio emission mechanisms is "jetted" from the ones where the mechanism is likely to be fundamentally different.
662. SDSS-GALEX QSO catalog
ID:
ivo://CDS.VizieR/J/AJ/140/1987
Title:
SDSS-GALEX QSO catalog
Short Name:
J/AJ/140/1987
Date:
21 Oct 2021
Publisher:
CDS
Description:
We discuss a sample of ~60000 objects from the combined Sloan Digital Sky Survey-Galaxy Evolution Explorer (SDSS-GALEX) database with UV-optical colors that should isolate QSOs in the redshift range 0.5-1.5. We use SDSS spectra of a subsample of ~4500 to remove stellar and galaxy contaminants in the sample to a very high level, based on the 7-band photometry. We discuss the distributions of redshift, luminosity, and reddening of the 19100 QSOs (~96%) that we estimate to be present in the final sample of 19812 point sources.
663. SDSS-III DR9 DLA catalogue
ID:
ivo://CDS.VizieR/J/A+A/547/L1
Title:
SDSS-III DR9 DLA catalogue
Short Name:
J/A+A/547/L1
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a study of the column density distribution and cosmological mass density of neutral gas from a survey of Damped Lyman-alpha systems in the Sloan Digital Sky Survey III Data Release 9.
664. SDSS J151349.52+035211.28 Xshooter spectra
ID:
ivo://CDS.VizieR/J/A+A/618/A184
Title:
SDSS J151349.52+035211.28 Xshooter spectra
Short Name:
J/A+A/618/A184
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the detection and detailed analysis of a diffuse molecular cloud at z_abs_=2.4636 towards the quasar SDSS J151349.52+035211.28 (hereafter J1513+0352) (zem~=2.68) observed with the X-shooter spectrograph at the Very Large Telescope. We measure very high column densities of atomic and molecular hydrogen, with logN(HI,H_2_)~=21.8,21.3. This is the highest H_2_ column density ever measured in an intervening damped Lyman-{alpha}system but we do not detect CO, implying log N(CO)/N(H_2_)<-7.8, which could be due to a low metallicity of the cloud. From the metal absorption lines, we derive the metallicity to be Z~=0.15Z_{sun}_ and determine the amount of dust by measuring the induced extinction of the background quasar light, AV~=0.4. We simultaneously detect Ly{alpha} emission at the same redshift, with a centroid located at a most probable impact parameter of only {rho}~=1.4kpc. We argue that the line of sight is therefore likely passing through the interstellar medium of a galaxy, as opposed to the circumgalactic medium. The relation between the surface density of gas and that of star formation seems to follow the global empirical relation derived in the nearby Universe although our constraints on the star formation rate and on the galaxy extent remain too loose to be conclusive. We study the transition from atomic to molecular hydrogen using a theoretical description based on the microphysics of molecular hydrogen.We use the derived chemical properties of the cloud and physical conditions (Tk~=90K and n~=250cm^-3^) derived through the excitation of H_2_ rotational levels and neutral carbon fine structure transitions to constrain the fundamental parameters that govern this transition. By comparing the theoretical and observed HI column densities, we are able to bring an independent constraint on the incident UV flux, which we find to be in agreement with that estimated from the observed star formation rate.
665. SDSS Lyman limit systems at z~3.5
ID:
ivo://CDS.VizieR/J/ApJ/718/392
Title:
SDSS Lyman limit systems at z~3.5
Short Name:
J/ApJ/718/392
Date:
21 Oct 2021
Publisher:
CDS
Description:
We perform a semi-automated survey for {tau}_912_>=2 Lyman limit systems (LLSs) in quasar spectra from the Sloan Digital Sky Survey, Data Release 7. From a starting sample of 2473 quasars with z_em_=3.6-5.0, we analyze 429 spectra meeting strict selection criteria for a total redshift path {Delta}z=93.8 and identify 190 intervening systems at z_LLS_>=3.3. We also perform a survey for proximate LLSs (PLLSs) and find that {l}_PLLS_(z) is systematically lower (~25%) than intervening systems.
666. SDSS & MMT obs. of extremely massive QSOs & gal.
ID:
ivo://CDS.VizieR/J/ApJ/871/57
Title:
SDSS & MMT obs. of extremely massive QSOs & gal.
Short Name:
J/ApJ/871/57
Date:
21 Oct 2021
Publisher:
CDS
Description:
Black hole mass scaling relations suggest that extremely massive black holes (EMBHs) with M_BH_>~10^9.4^M_{sun}_ are found in the most massive galaxies with M_star_>~10^11.6^M_{sun}_, which are commonly found in dense environments, like galaxy clusters. Therefore, one can expect that there is a close connection between active EMBHs and dense environments. Here, we study the environments of 9461 galaxies and 2943 quasars at 0.24<~z<~0.40, among which 52 are extremely massive quasars with log(M_BH_/M_{sun}_)>=~9.4, using Sloan Digital Sky Survey and MMT Hectospec data. We find that, on average, both massive quasars and massive galaxies reside in environments more than ~2 times as dense as those of their less massive counterparts with log(M_BH_/M_{sun}_)<~9.0. However, massive quasars reside in environments about ~2 times less dense than inactive galaxies with log(M_BH_/M_{sun}_)>=9.4, and only about one third of massive quasars are found in galaxy clusters, while about two thirds of massive galaxies reside in such clusters. This indicates that massive galaxies are a much better signpost for galaxy clusters than massive quasars. The prevalence of massive quasars in moderate to low density environments is puzzling, considering that several simulation results show that these quasars appear to prefer dense environments. Several possible reasons for this discrepancy are discussed, although further investigation is needed to obtain a definite explanation.
667. SDSS QSO DR7 and DR9
ID:
ivo://CDS.VizieR/J/A+A/616/A97
Title:
SDSS QSO DR7 and DR9
Short Name:
J/A+A/616/A97
Date:
21 Oct 2021
Publisher:
CDS
Description:
The explosion of data in recent years has generated an increasing need for new analysis techniques in order to extract knowledge from massive data-sets. Machine learning has proved particularly useful to perform this task. Fully automatized methods (e.g. deep neural networks) have recently gathered great popularity, even though those methods often lack physical interpretability. In contrast, feature based approaches can provide both well-performing models and understandable causalities with respect to the correlations found between features and physical processes. Efficient feature selection is an essential tool to boost the performance of machine learning models. In this work, we propose a forward selection method in order to compute, evaluate, and characterize better performing features for regression and classification problems. Given the importance of photometric redshift estimation, we adopt it as our case study. We synthetically created 4520 features by combining magnitudes, errors, radii, and ellipticities of quasars, taken from the Sloan Digital Sky Survey (SDSS). We apply a forward selection process, a recursive method in which a huge number of feature sets is tested through a k-Nearest-Neighbours algorithm, leading to a tree of feature sets. The branches of the feature tree are then used to perform experiments with the random forest, in order to validate the best set with an alternative model. We demonstrate that the sets of features determined with our approach improve the performances of the regression models significantly when compared to the performance of the classic features from the literature. The found features are unexpected and surprising, being very different from the classic features. Therefore, a method to interpret some of the found features in a physical context is presented. The feature selection methodology described here is very general and can be used to improve the performance of machine learning models for any regression or classification task.
668. SDSS QSO DR14 spectral properties
ID:
ivo://CDS.VizieR/J/ApJS/249/17
Title:
SDSS QSO DR14 spectral properties
Short Name:
J/ApJS/249/17
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present measurements of the spectral properties for a total of 526,265 quasars, out of which 63% have a continuum signal-to-noise ratio >3pixel^-1^, selected from the fourteenth data release of the Sloan Digital Sky Survey (SDSS-DR14) quasar catalog. We performed a careful and homogeneous analysis of the SDSS spectra of these sources to estimate the continuum and line properties of several emission lines such as H{alpha}, H{beta}, H{gamma}, MgII, CIII], CIV, and Ly{alpha}. From the derived emission line parameters, we estimated single-epoch virial black hole masses (M_BH_) for the sample using H{beta}, MgII, and CIV emission lines. The sample covers a wide range in bolometric luminosity (logLbol; erg/s) between 44.4 and 47.3 and logM_BH_ between 7.1 and 9.9M_{sin}_. Using the ratio of Lbol to the Eddington luminosity as a measure of the accretion rate, the logarithm of the accretion rate is found to be in the range between -2.06 and 0.43. We performed several correlation analyses between different emission line parameters and found them to match the correlation known earlier using smaller samples. We note that strong FeII sources with a large Balmer line width and highly accreting sources with large M BH are rare in our sample. We make an extended and complete catalog available online that contains various spectral properties of 526,265 quasars derived in this work along with other properties culled from the SDSS-DR14 quasar catalog.
669. SDSS QSOs at z<0.8. II. New spectroscopic obs.
ID:
ivo://CDS.VizieR/J/ApJS/221/7
Title:
SDSS QSOs at z<0.8. II. New spectroscopic obs.
Short Name:
J/ApJS/221/7
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present new spectroscopic observations that are part of our continuing monitoring campaign of 88 quasars at z<0.7 whose broad H{beta} lines are offset from their systemic redshifts by a few thousand km/s. These quasars have been considered as candidates for hosting supermassive black hole binaries (SBHBs) by analogy with single-lined spectroscopic binary stars. We present the data and describe our improved analysis techniques, which include an extensive evaluation of uncertainties. We also present a variety of measurements from the spectra that are of general interest and will be useful in later stages of our analysis. Additionally, we take this opportunity to study the variability of the optical continuum and integrated flux of the broad H{beta} line. We compare the variability properties of the SBHB candidates to those of a sample of typical quasars with similar redshifts and luminosities observed multiple times during the Sloan Digital Sky Survey. We find that the variability properties of the two samples are similar (variability amplitudes of 10%-30% on timescales of approximately 1-7 years) and that their structure functions can be described by a common model with parameters characteristic of typical quasars. These results suggest that the broad-line regions of SBHB candidates have a similar extent as those of typical quasars. We discuss the implications of this result for the SBHB scenario and the ensuing constraints on the orbital parameters.
670. SDSS Quasar Catalog, DR9Q
ID:
ivo://CDS.VizieR/VII/269
Title:
SDSS Quasar Catalog, DR9Q
Short Name:
VII/269
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present the Data Release 9 Quasar (DR9Q) catalog from the Baryon Oscillation Spectroscopic Survey (BOSS) of the Sloan Digital Sky Survey III. The catalog includes all BOSS objects that were targeted as quasar candidates during the survey, are spectroscopically confirmed as quasars via visual inspection. This catalog contains 87,822 quasars (78,086 are new discoveries) detected over 3,275{deg}^2^ with robust identification and redshift measured by a combination of principal component eigenspectra newly derived from a training set of 8,632 spectra from SDSS-DR7. The number of quasars with z>2.15 (61,931) is 2.8 times larger than the number of z>2.15 quasars previously known. Redshifts and FWHMs are provided for the strongest emission lines (CIV, CIII], MgII). The catalog identifies 7,533 broad absorption line quasars and gives their characteristics. For each object the catalog presents five-band (u,g,r,i,z) CCD-based photometry with typical accuracy of 0.03mag, and information on the morphology and selection method. The catalog also contains X-ray, ultraviolet, near-infrared, and radio emission properties of the quasars, when available, from other large-area surveys. We also provide a supplemental list of an additional 949 quasars that have been identified, among galaxy targets of the BOSS or among quasar targets after DR9 was frozen.