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5811. SDSS DR7 groups of galaxies
ID:
ivo://CDS.VizieR/J/A+A/514/A102
Title:
SDSS DR7 groups of galaxies
Short Name:
J/A+A/514/A102
Date:
21 Oct 2021
Publisher:
CDS
Description:
We extract groups of galaxies as flux-limited and volume-limited samples from the SDSS Data Release 7 to study the supercluster-void network and environmental properties of groups therein. Volume-limited catalogues are particularly useful for comparison of numerical simulations of dark matter halos and the large-scale structure with observations. Extraction of a volume-limited sample of galaxies and groups requires special care to avoid excluding too much observational data. We use a modified friends-of-friends (FoF) method with a slightly variable linking length to obtain a preliminary flux-limited sample. We use the flux-limited groups as the basic sample to include as many galaxies as possible in the volume-limited samples. To determine the scaling of the linking length we calibrated group sizes and mean galaxy number densities within groups by magnitude dilution of a nearby group sub-sample to follow the properties of groups with higher luminosity limits. Our final flux-limited sample contains 78800 groups, and volume-limited subsamples with absolute magnitude limits M_r_=-18, -19, -20, and -21 contain 5463, 12590, 18973, and 9139 groups, respectively, in the DR7 main galaxy main area survey. The spatial number densities of our groups within the subsamples, as well as the mean sizes and rms velocities of our groups practically do not change from sub-sample to sub-sample. This means that the catalogues are homogeneous and well suited for comparison with simulations.
5812. SDSS-DR7 isolated galaxy morphologies
ID:
ivo://CDS.VizieR/J/ApJS/220/3
Title:
SDSS-DR7 isolated galaxy morphologies
Short Name:
J/ApJS/220/3
Date:
21 Oct 2021
Publisher:
CDS
Description:
Isolated galaxies in low-density regions are significant in the sense that they are least affected by the hierarchical pattern of galaxy growth and interactions with perturbers, at least for the last few gigayears. To form a comprehensive picture of the star-formation history of isolated galaxies, we constructed a catalog of isolated galaxies and their comparison sample in relatively denser environments. The galaxies are drawn from the Sloan Digital Sky Survey Data Release 7 in the redshift range of 0.025<z<0.044. We performed a visual inspection and classified their morphology following the Hubble classification scheme. For the spectroscopic study, we make use of the catalog provided by Oh et al. (2011ApJS..195...13O). We confirm most of the earlier understanding on isolated galaxies. The most remarkable additional results are as follows. Isolated galaxies are dominantly late type with the morphology distribution (E:S0:S:Irr)=(9.9:11.3:77.6:1.2)%. The frequency of elliptical galaxies among isolated galaxies is only a third of that of the comparison sample. Most of the photometric and spectroscopic properties are surprisingly similar between the isolated and comparison samples. However, early-type isolated galaxies are less massive by 50% and younger (by H{beta}) by 20% than their counterparts in the comparison sample. This can be explained as a result of different merger and star-formation histories for differing environments in the hierarchical merger paradigm.
5813. SDSS-DR5 low-mass star spectroscopic sample
ID:
ivo://CDS.VizieR/J/AJ/135/785
Title:
SDSS-DR5 low-mass star spectroscopic sample
Short Name:
J/AJ/135/785
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a spectroscopic analysis of over 38000 low-mass stars from the Sloan Digital Sky Survey (SDSS) Data Release 5 (DR5). Analysis of this unprecedentedly large sample confirms the previously detected decrease in the fraction of magnetically active stars (as traced by H{alpha} emission) as a function of vertical distance from the Galactic Plane. The magnitude and slope of this effect varies as a function of spectral type. Using simple 1-D dynamical models, we demonstrate that the drop in activity fraction can be explained by thin disk dynamical heating and a rapid decrease in magnetic activity. The timescale for this rapid activity decrease changes according to the spectral type. By comparing our data to the simulations, we calibrate the age-activity relation at each M dwarf spectral type. We also present evidence for a possible decrease in the metallicity as a function of height above the Galactic Plane. In addition to our activity analysis, we provide line measurements, molecular band indices, colors, radial velocities, 3-D space motions and mean properties as a function of spectral type for the SDSS DR5 low-mass star sample.
5814. SDSS-DR5 quasar catalog
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.
5815. SDSS DR7 white dwarf catalog
ID:
ivo://CDS.VizieR/J/ApJS/204/5
Title:
SDSS DR7 white dwarf catalog
Short Name:
J/ApJS/204/5
Date:
21 Oct 2021
Publisher:
CDS
Description:
We present a new catalog of spectroscopically confirmed white dwarf stars from the Sloan Digital Sky Survey (SDSS) Data Release 7 spectroscopic catalog. We find 20407 white dwarf spectra, representing 19712 stars, and provide atmospheric model fits to 14120 DA and 1011 DB white dwarf spectra from 12843 and 923 stars, respectively. These numbers represent more than a factor of two increase in the total number of white dwarf stars from the previous SDSS white dwarf catalogs based on DR4 data. Our distribution of subtypes varies from previous catalogs due to our more conservative, manual classifications of each star in our catalog, supplementing our automatic fits. In particular, we find a large number of magnetic white dwarf stars whose small Zeeman splittings mimic increased Stark broadening that would otherwise result in an overestimated logg if fit as a non-magnetic white dwarf. We calculate mean DA and DB masses for our clean, non-magnetic sample and find the DB mean mass is statistically larger than that for the DAs.
5816. SDSS Early-Type Galaxies Catalog
ID:
ivo://CDS.VizieR/J/AJ/125/1817
Title:
SDSS Early-Type Galaxies Catalog
Short Name:
J/AJ/125/1817
Date:
21 Oct 2021
Publisher:
CDS
Description:
A sample of nearly 9000 early-type galaxies, in the redshift range 0.01<=z<=0.3, was selected from the Sloan Digital Sky Survey (SDSS) using morphological and spectral criteria. The paper describes how the sample was selected, presents examples of images and seeing-corrected fits to the observed surface brightness profiles, describes our method for estimating K-corrections, and shows that the SDSS spectra are of sufficiently high quality to measure velocity dispersions accurately. It also provides catalogs of the measured photometric and spectroscopic parameters. In related papers, these data are used to study how early-type galaxy observables, including luminosity, effective radius, surface brightness, color, and velocity dispersion, are correlated with one another.
5817. SDSS galaxies morphological classification
ID:
ivo://CDS.VizieR/J/A+A/648/A122
Title:
SDSS galaxies morphological classification
Short Name:
J/A+A/648/A122
Date:
22 Feb 2022
Publisher:
CDS
Description:
Machine learning methods are effective tools in astronomical tasks for classifying objects by their individual features. One of the promising utilities is related to the morphological classification of galaxies at different redshifts. We use the photometry-based approach for the SDSS data (1) to exploit five supervised machine learning techniques and define the most effective among them for the automated galaxy morphological classification; (2) to test the influence of photometry data on morphology classification; (3) to discuss problem points of supervised machine learning and labeling bias; and (4) to apply the best fitting machine learning methods for revealing the unknown morphological types of galaxies from the SDSS DR9 at z<0.1. We used different galaxy classification techniques: human labeling, multi-photometry diagrams, naive Bayes, logistic regression, support-vector machine, random forest, k-nearest neighbors. We present the results of a binary automated morphological classification of galaxies conducted by human labeling, multi-photometry, and five supervised machine learning methods. We applied it to the sample of galaxies from the SDSS DR9 with redshifts of 0.02<z<0.1 and absolute stellar magnitudes of -24mag<Mr<-19.4mag. For the analysis we used absolute magnitudes Mu, Mg, Mr, Mi, Mz; color indices Mu-Mr, Mg-Mi, Mu-Mg, Mr-Mz; and the inverse concentration index to the center R50/R90. We determined the ability of each method to predict the morphological type, and verified various dependencies of the method's accuracy on redshifts, human labeling, morphological shape, and overlap of different morphological types for galaxies with the same color indices. We find that the morphology based on the supervised machine learning methods trained over photometric parameters demonstrates significantly less bias than the morphology based on citizen-science classifiers. The support-vector machine and random forest methods with Scikit-learn software machine learning library in Python provide the highest accuracy for the binary galaxy morphological classification. Specifically, the success rate is 96.4% for support-vector machine (96.1% early E and 96.9% late L types) and 95.5% for random forest (96.7% early E and 92.8% late L types). Applying the support-vector machine for the sample of 316 031 galaxies from the SDSS DR9 at z<0.1 with unknown morphological types, we found 139659 E and 176372 L types among them.
5818. 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.
5819. SDSS-II SN Ia BVRI photometry
ID:
ivo://CDS.VizieR/J/MNRAS/465/1274
Title:
SDSS-II SN Ia BVRI photometry
Short Name:
J/MNRAS/465/1274
Date:
21 Oct 2021
Publisher:
CDS
Description:
We have analysed multiband light curves of 328 intermediate-redshift (0.05<=z<0.24) Type Ia supernovae (SNe Ia) observed by the Sloan Digital Sky Survey-II Supernova Survey. The multiband light curves were parametrized by using the multiband stretch method, which can simply parametrize light-curve shapes and peak brightness without dust extinction models. We found that most of the SNe Ia that appeared in red host galaxies (u-r>2.5) do not have a broad light-curve width and the SNe Ia that appeared in blue host galaxies (u-r<2.0) have a variety of light-curve widths. The Kolmogorov-Smirnov test shows that the colour distribution of SNe Ia appearing in red/blue host galaxies is different (a significance level of 99.9 per cent). We also investigate the extinction law of host galaxy dust. As a result, we find that the value of Rv derived from SNe Ia with medium light-curve widths is consistent with the standard Galactic value, whereas the value of Rv derived from SNe Ia that appear in red host galaxies becomes significantly smaller. These results indicate that there may be two types of SNe Ia with different intrinsic colours, and that they are obscured by host galaxy dust with two different properties.
5820. SDSS-II SN Survey: SNe II-P standardization
ID:
ivo://CDS.VizieR/J/ApJ/708/661
Title:
SDSS-II SN Survey: SNe II-P standardization
Short Name:
J/ApJ/708/661
Date:
21 Oct 2021
Publisher:
CDS
Description:
We apply the Standardized Candle Method (SCM) for Type II Plateau supernovae (SNe II-P), which relates the velocity of the ejecta of a SN to its luminosity during the plateau, to 15 SNe II-P discovered over the three season run of the Sloan Digital Sky Survey-II Supernova Survey. The redshifts of these SNe - 0.027<z<0.144 - cover a range hitherto sparsely sampled in the literature; in particular, our SNe II-P sample contains nearly as many SNe in the Hubble flow (z>0.01) as all of the current literature on the SCM combined. We find that the SDSS SNe have a very small intrinsic I-band dispersion (0.22mag), which can be attributed to selection effects. When the SCM is applied to the combined SDSS-plus-literature set of SNe II-P, the dispersion increases to 0.29mag, larger than the scatter for either set of SNe separately. We show that the standardization cannot be further improved by eliminating SNe with positive plateau decline rates, as proposed in Poznanski et al. (2009ApJ...694.1067P). We thoroughly examine all potential systematic effects and conclude that for the SCM to be useful for cosmology, the methods currently used to determine the FeII velocity at day 50 must be improved, and spectral templates able to encompass the intrinsic variations of Type II-P SNe will be needed.