J/A+A/xxx/xxx Groups and clusters of galaxies in the SDSS DR8 (Tempel+, 2012) ================================================================================ Groups and clusters of galaxies in the SDSS DR8. Value-added catalogues Tempel E., Tago E., Liivam"agi L.J. =2011arXiv1112.4648T arXiv:1112.4648 ================================================================================ ADC_Keywords: Clusters, galaxy ; Galaxy catalogs Keywords: catalogs - galaxies: clusters: general - galaxies: groups: general - galaxies: statistics - large-scale structure of Universe - cosmology: observations Abstract: 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). Description: Galaxy and group catalogues based on SDSS DR 8 data are presented. File Summary: -------------------------------------------------------------------------------- FileName Lrecl Records Explanations -------------------------------------------------------------------------------- readme.txt 80 . this file dr8_ggc.fits -- . fits binary table file dr8_ggc.tar.gz -- . ascii tables -------------------------------------------------------------------------------- See also: J/A+A/514/A102 : Groups of galaxies in the SDSS Data Release 7. Flux- and volume-limited samples (Tago+, 2010) J/A+A/479/927 : Groups of galaxies in the SDSS Data Release 5. A group- finder and a catalogue (Tago+, 2008) Description of the galaxy catalogue (column numbers in square brackets): -------------------------------------------------------------------------------- 1. [1] id - a unique identification number for galaxies, used by us; 2. [2] idcl - the group/cluster id; 3. [3] nrich - the richness of the group the galaxy belongs to; 4. [4] redshift - the redshift, corrected to the CMB rest frame; 5. [5] dist - the co-moving distance in units of Mpc/h (calculated directly from redshift); 6. [6] distcl - the co-moving distance to the group/cluster centre, where the galaxy belongs to, in units of Mpc/h, calculated as an average over all galaxies, belonging to the group/cluster; 7. [7-8] ra, dec - the right ascension and declination (deg); 8. [9-10] lon, lat - the galactic longitude and latitude (deg); 9. [11-12] eta, lam - the SDSS survey coordinates eta and lambda (deg); 10. [13-17] mag_x - Galactic extinction corrected Petrosian magnitude (x=ugriz); 11. [18-22] absmag_x - the absolute magnitude of the galaxy, k+e-corrected (x = ugriz filters, in units of mag + 5 log10(h)); 12. [23-27] kcor_x - the k-correction by KCORRECT algorithm (x=ugriz filters); 13. [28] lumr - the observed luminosity in the r-band in units of 10^10L_sun/h^2 where Msun = 4.64 (Blanton & Roweis 2007); 14. [29] w - the weight factor for the galaxy (w*lumr was used to calculate the luminosity density field); 15. [30] rank - the galaxy rank in its group, calculated based on the galaxy luminosity: for the most luminous galaxy, the rank is 1; 16. [31-35] dena - the normalised environmental density of the galaxy for various smoothing scales (a = 1, 2, 4, 8, 16 Mpc/h); for galaxies outside our survey mask we use the value -999, indicating that the galaxy is outside the mask; 17. [36] edgedist - the co-moving distance of the galaxy from the border of the survey mask; 18. [37] morf - the morphology of the galaxy (0- unclear, 1- spiral, 2- ellipt) 19. [38] hcearly - the Huertas-Company et al. (2011) mark of being an early type galaxy; 20. [39] dr8objid - the SDSS DR8 photometric object identification number; 21. [40] dr8specobjid - the SDSS DR8 spectroscopic object identification number; 22. [41] iddr7 - an unique identification number to link with the en- tries in our previous DR7 group catalogue; 23. [42] zobs - the observed redshift (without CMB correction); 24. [43] distcor - the co-moving distance of the galaxy where the finger-of-god effect is suppressed (as used in luminosity density field calculations); 25. [44] flaggc - if greater than zero, indicates that the galaxy has a missing (with unknown redshift) neighbour due to a fibre collision. -------------------------------------------------------------------------------- Description of the group/cluster catalogue (column numbers in square brackets): -------------------------------------------------------------------------------- 1. [1] idcl - the group/cluster id; 2. [2] nrich - the group richness, number of observed galaxies in group; 3. [3] zcl - the CMB-corrected redshift of group; 4. [4] distcl - the co-moving distance to the group centre (Mpc/h); 5. [5-6] racl, deccl - the equatorial coordinates, the right ascension and declination (deg); 6. [7-8] loncl, latcl - the galactic longitude and latitude (deg); 7. [9-10] etacl, lamcl - the SDSS survey coordinates eta and lambda (deg); 8. [11] sizesky - the maximum linear size of the group in the sky (in physical coordinates, Mpc/h); 9. [12] rvir - the virial radius in Mpc/h (the projected harmonic mean, in physical coordinates); 10. [13] sigma_sky - the rms deviation of the projected distance in the sky from the group centre (physical coordinates, Mpc/h); 11. [14] sigma_v - the rms radial velocity deviation (sigma_V in physical coordinates, in km/s ); 12. [15] lumobs_r - the observed luminosity, the sum of observed galaxy luminosities (10^10L_sun/h^2); 13. [16] lumtot_r - the estimated total luminosity of the group (10^10Lsun/h^2), the observed luminosity multiplied by a weight factor; 14. [17] dlink - the co-moving linking length used to define the group (Mpc/h); 15. [18-22] denacl - the environmental density for the group for various smoothing scales (a = 1, 2, 4, 8, 16 Mpc/h), averaged over group galaxies inside the survey mask; 16. [23] edgedistcl - the minimum co-moving distance of group galaxies from the edge of the survey mask. Zero, if at least one member is outside the survey mask. 17. [24] flaggccl - if greater than zero, indicates that the group contains potentially missing (with unknown red- shift) galaxies due to the fibre collisions. -------------------------------------------------------------------------------- ================================================================================ (End) Elmo Tempel [Tartu Observatory, Estonia] 01-Feb-2012