- ID:
- ivo://CDS.VizieR/J/A+A/540/A106
- Title:
- SDSS-DR8 groups and clusters of galaxies
- Short Name:
- J/A+A/540/A106
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We create a new catalogue of groups and clusters for the SDSS Data Release 8 sample. We add environmental parameters to our catalogue, together with other galaxy parameters (e.g., morphology), missing from our previous catalogues. We use a modified friends-of-friends (FoF) method with a variable linking length in the transverse and radial directions to eliminate selection effects and to find reliably as many groups as possible to track the supercluster network. We use the groups of galaxies as a basis to determine the luminosity density field. We take into account various selection effects caused by a magnitude limited sample. Our final sample contains 576493 galaxies and 77858 groups. The group catalogue is available at http://www.aai.ee/~elmo/dr8groups/ and from the Strasbourg Astronomical Data Center (CDS).
Number of results to display per page
Search Results
- 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.
- ID:
- ivo://CDS.VizieR/J/AJ/129/2062
- Title:
- SDSS DR1 isolated galaxies
- Short Name:
- J/AJ/129/2062
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present a new catalog of isolated galaxies obtained through an automated systematic search. These 2980 isolated galaxies were found in ~2099{deg}^2^ of sky in the Sloan Digital Sky Survey Data Release 1 (SDSS DR1, http://www.sdss.org/dr1/) photometry. The selection algorithm, implementing a variation on the criteria developed by Karachentseva in 1973, proved to be very efficient and fast. This catalog will be useful for studies of the general galaxy characteristics. Here we report on our results.
- ID:
- ivo://CDS.VizieR/J/AJ/135/10
- Title:
- SDSS-DR4/RASS source matching
- Short Name:
- J/AJ/135/10
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The current view of galaxy formation holds that all massive galaxies harbor a massive black hole at their center, but that these black holes are not always in an actively accreting phase. X-ray emission is often used to identify accreting sources, but for galaxies that are not harboring quasars (low-luminosity active galaxies), the X-ray flux may be weak, or obscured by dust. To aid in the understanding of weakly accreting black holes in the local universe, a large sample of galaxies with X-ray detections is needed. We cross-match the ROSAT All Sky Survey (RASS) with galaxies from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) to create such a sample. Because of the high SDSS source density and large RASS positional errors, the cross-matched catalog is highly contaminated by random associations. We investigate the overlap of these surveys and provide a statistical test of the validity of RASS-SDSS galaxy cross-matches.
- 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.
- 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.
- ID:
- ivo://CDS.VizieR/J/MNRAS/465/1831
- Title:
- SDSS-IV eBOSS ELG UgrizW photometry
- Short Name:
- J/MNRAS/465/1831
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We present two wide-field catalogues of photometrically selected emission line galaxies (ELGs) at z~=0.8 covering about 2800deg^2^ over the south galactic cap. The catalogues were obtained using a Fisher discriminant technique described in a companion paper. The two catalogues differ by the imaging used to define the Fisher discriminant: the first catalogue includes imaging from the Sloan Digital Sky Survey and the Wide-field InfraredSurvey Explorer, the second also includes information from the South Galactic Cap U-band Sky Survey. Containing respectively 560045 and 615601 objects, they represent the largest ELG catalogues available today and were designed for the ELG programme of the extended Baryon Oscillation Spectroscopic Survey (eBOSS). We study potential sources of systematic variation in the angular distribution of the selected ELGs due to fluctuations of the observational parameters. We model the influence of the observational parameters using a multivariate regression and implement a weighting scheme which allows effective removal of all of the systematic errors induced by the observational parameters. We show that fluctuations in the imaging zero-points of the photometric bands have minor impact on the angular distribution of objects in our catalogues. We compute the angular clustering of both catalogues and show that our weighting procedure effectively removes spurious clustering on large scales. We fit a model to the small-scale angular clustering, showing that the selections have similar biases of 1.35/Da(z) and 1.28/Da(z). Both catalogues are publicly available.
- ID:
- ivo://CDS.VizieR/J/A+A/592/A121
- Title:
- SDSS-IV eBOSS emission-line galaxy pilot survey
- Short Name:
- J/A+A/592/A121
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- The Sloan Digital Sky Survey IV extended Baryonic Oscillation Spectroscopic Survey (SDSS-IV/eBOSS) will observe 195,000 emission-line galaxies (ELGs) to measure the Baryonic Acoustic Oscillation standard ruler (BAO) at redshift 0.9. To test different ELG selection algorithms, based on data from several imaging surveys, 9,000 spectra were observed with the SDSS spectrograph as a pilot survey. First, using visual inspection and redshift quality flags, we find that the automated spectroscopic redshifts assigned by the pipeline meet the quality requirements for a robust BAO measurement. Also, we show the correlations between sky emission, signal-to-noise ratio in the emission lines and redshift error. Then we provide a detailed description of each target selection algorithm tested and compare them with the requirements of the eBOSS experiment. As a result, we provide robust redshift distributions for the different target selection schemes tested. Finally, we infer two optimal target selection algorithms to be applied on DECam photometry that fulfill the eBOSS survey electronic efficiency requirements.
- ID:
- ivo://CDS.VizieR/J/MNRAS/443/3528
- Title:
- SDSS peculiar galaxy pairs list
- Short Name:
- J/MNRAS/443/3528
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- We applied computational tools for automatic detection of peculiar galaxy pairs. We first detected in Sloan Digital Sky Survey DR7 ~400000 galaxy images with i magnitude <18 that had more than one point spread function, and then applied a machine learning algorithm that detected ~26000 galaxy images that had morphology similar to the morphology of galaxy mergers. That data set was mined using a novelty detection algorithm, producing a short list of 500 most peculiar galaxies as quantitatively determined by the algorithm. Manual examination of these galaxies showed that while most of the galaxy pairs in the list were not necessarily peculiar, numerous unusual galaxy pairs were detected. In this paper, we describe the protocol and computational tools used for the detection of peculiar mergers, and provide examples of peculiar galaxy pairs that were detected.
- ID:
- ivo://CDS.VizieR/J/MNRAS/433/2986
- Title:
- SDSSRC3 sample morphological classifications
- Short Name:
- J/MNRAS/433/2986
- Date:
- 21 Oct 2021
- Publisher:
- CDS
- Description:
- Galaxies grow primarily via accretion-driven star formation in discs and merger-driven growth of bulges. These processes are implicit in semi-analytical models of galaxy formation, with bulge growth in particular relating directly to the hierarchical build-up of haloes and their galaxies. In this paper, we consider several implementations of two semi-analytical models. Focusing on implementations in which bulges are formed during mergers only, we examine the fractions of elliptical galaxies and both passive and star-forming disc galaxies as functions of stellar and halo mass, for central and satellite systems. This is compared to an observational cross-matched Sloan Digital Sky Survey+Third Reference Catalog of Bright Galaxies z~0 sample of galaxies with accurate visual morphological classifications and M*>10^10.5^M_{sun}_. The models qualitatively reproduce the observed increase of elliptical fraction with stellar mass, and with halo mass for central galaxies, supporting the idea that observed ellipticals form during major mergers. However, the overall elliptical fraction produced by the models is much too high compared with the z~0 data. Since the 'passive' - i.e. non-star-forming - fractions are approximately reproduced, and since the fraction which are star-forming disc galaxies is also reproduced, the problem is that the models overproduce ellipticals at the expense of passive S0 and spiral galaxies. Bulge growth implementations (tuned to reproduce simulations) which allow the survival of residual discs in major mergers still destroy too much of the disc. Increasing the lifetime of satellites, or allowing significant disc regrowth around merger remnants, merely increases the fraction of star-forming disc galaxies. Instead, it seems necessary to reduce the mass ratios of merging galaxies, so that most mergers produce modest bulge growth in disc galaxy remnants instead of ellipticals. This could be a natural consequence of tidal stripping of stars from infalling satellite galaxies, a process not considered in our models. However, a high efficiency of quenching during and/or subsequent to minor mergers is still required to keep the passive fraction high.
