- 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.
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Search Results
- 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.
- 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/MNRAS/422/25
- Title:
- SDSS DR7 groups, clusters and filaments
- Short Name:
- J/MNRAS/422/25
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We have developed a multiscale structure identification algorithm for the detection of overdensities in galaxy data that identifies structures having radii within a user-defined range. Our "multiscale probability mapping" technique combines density estimation with a shape statistic to identify local peaks in the density field. This technique takes advantage of a user-defined range of scale sizes, which are used in constructing a coarse-grained map of the underlying fine-grained galaxy distribution, from which overdense structures are then identified. In this study we have compiled a catalogue of groups and clusters at 0.025<z<0.24 based on the Sloan Digital Sky Survey (SDSS), Data Release 7, quantifying their significance and comparing with other catalogues. Most measured velocity dispersions for these structures lie between 50 and 400km/s. A clear trend of increasing velocity dispersion with radius from 0.2 to 1Mpc/h is detected, confirming the lack of a sharp division between groups and clusters. A method for quantifying elongation is also developed to measure the elongation of group and cluster environments. By using our group and cluster catalogue as a coarse-grained representation of the galaxy distribution for structure sizes of <~1Mpc/h, we identify 53 filaments (from an algorithmically derived set of 100 candidates) as elongated unions of groups and clusters at 0.025<z<0.13. These filaments have morphologies that are consistent with previous samples studied.
- ID:
- ivo://CDS.VizieR/J/MNRAS/354/L31
- Title:
- SDSS DR2 QSO and DLA properties
- Short Name:
- J/MNRAS/354/L31
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We use Sloan Digital Sky Survey (SDSS) Data Release 2 quasi-stellar object (QSO) spectra to constrain the dust-reddening caused by intervening damped Lyman {alpha} systems (DLAs). Comparing the spectral index distribution of a 70 sight-line DLA sample with that of a large control sample reveals no evidence for dust-reddening at z~3.
- ID:
- ivo://CDS.VizieR/J/MNRAS/452/4153
- Title:
- SDSS DR12 QSOs [OIII] doublet
- Short Name:
- J/MNRAS/452/4153
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- From the Sloan Digital Sky Survey (SDSS) Data Release 12, which covers the full Baryonic Oscillation Spectroscopic Survey (BOSS) footprint, we investigate the possible variation of the fine-structure constant over cosmological time-scales. We analyse the largest quasar sample considered so far in the literature, which contains 13175 spectra (10363 from SDSS-III/BOSS DR12+2812 from SDSS-II DR7) with redshift z<1. We apply the emission-line method on the [OIII] doublet ({lambda}{lambda}4960, 5008{AA}) and obtain {Delta}{alpha}/{alpha}=(0.9+/-1.8)x10^-5^ for the relative variation of the fine-structure constant. We also investigate the possible sources of systematics: misidentification of the lines, sky OH lines, H{beta} and broad line contamination, Gaussian and Voigt fitting profiles, optimal wavelength range for the Gaussian fits, chosen polynomial order for the continuum spectrum, signal-to-noise ratio and good quality of the fits. The uncertainty of the measurement is dominated by the sky subtraction. The results presented in this work, being systematics limited, have sufficient statistics to constrain robustly the variation of the fine-structure constant in redshift bins ({Delta}z~0.06) over the last 7.9Gyr. In addition, we study the [NeIII] doublet ({lambda}{lambda}3869, 3968{AA}) present in 462 quasar spectra and discuss the systematic effects on using these emission lines to constrain the fine-structure constant variation. Better constraints on {Delta}{alpha}/{alpha}(<10^-6^) using the emission-line method would be possible with high-resolution spectroscopy and large galaxy/qso surveys.
- ID:
- ivo://CDS.VizieR/VII/252
- Title:
- SDSS-DR5 quasar catalog
- Short Name:
- VII/252
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The fourth edition of the Sloan Digital Sky Survey (SDSS) Quasar Catalog, made from the SDSS Fifth Data Release, contains 77,429 objects; this is an increase of over 30,000 entries since the previous edition (Schneider et al., Cat. <VII/243>). The catalog consists of the objects in the SDSS Fifth Data Release that have luminosities larger than M_i_=-22.0 (in a cosmology with Ho=70km.s-1.Mpc-1, {Omega}_M_=0.3, and {Omega}_{Lambda}_=0.7), have at least one emission line with FWHM larger than 1000km.s-1 or have interesting or complex absorption features, are fainter than i~15.0, and have highly reliable redshifts. The area covered by the catalog is about 5740deg^2^. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.48; the catalog includes 891 quasars at redshifts greater than 4, of which 36 are at redshifts greater than 5. Approximately half of the catalog quasars have i<19; nearly all have i<21. For each object the catalog presents positions accurate to better than 0.2" rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03mag, and information on the morphology and selection method. The catalog also contains basic radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200{AA} at a spectral resolution of about 2000; the spectra can be retrieved from the public database using the information provided in the catalog. The average SDSS colors of quasars as a function of redshift, derived from the catalog entries, are presented in tabular form. Approximately 96% of the objects in the catalog were discovered by the SDSS.
- ID:
- ivo://CDS.VizieR/VII/243
- Title:
- SDSS quasar catalog. III.
- Short Name:
- VII/243
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The catalog consists of the 46,420 objects in the SDSS Third Data Release that have luminosities larger than M_i_=-22 (in a cosmology with Ho=70km/s/Mpc, {Omega}_M_=0.3 and {Omega}_{Lambda}_=0.7), have at least one emission line with FWHM larger than 1000 km/s or are unambiguously broad absorption line quasars, are fainter than i=15.0 and have highly reliable redshifts. The area covered by the catalog is about 4188 deg^2^. The quasar redshifts range from 0.08 to 5.41, with a median value of 1.47; the high-redshift sample includes 520 quasars at redshifts greater than four, of which 17 are at redshifts greater than five. For each object the catalog presents positions accurate to better than 0.2" rms per coordinate, five-band (ugriz) CCD-based photometry with typical accuracy of 0.03 mag, and information on the morphology and selection method. The catalog also contains radio, near-infrared, and X-ray emission properties of the quasars, when available, from other large-area surveys. The calibrated digital spectra cover the wavelength region 3800-9200{AA} at a spectral resolution of about 2000; the spectra can be retrieved from the public database using the information provided in the catalog. A total of 44,221 objects in the catalog were discovered by the SDSS; 28,400 of the SDSS discoveries are reported here for the first time.
