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Title:
Galaxy Groups in the SDSS DR4. II. Halo Occupation Statistics
Authors:
Yang, Xiaohu; Mo, H. J.; van den Bosch, Frank C.
Affiliation:
AA(Shanghai Astronomical Observatory, Partner Group of MPA, Nandan Road 80, Shanghai 200030, China; .; Joint Institute for Galaxy and Cosmology (JOINGC) of Shanghai Astronomical Observatory and University of Science and Technology of China.), AB(Department of Astronomy, University of Massachusetts, Amherst, MA 01003-9305.), AC(Max-Planck-Institute for Astronomy, Königstuhl 17, D-69117 Heidelberg, Germany.)
Publication:
The Astrophysical Journal, Volume 676, Issue 1, pp. 248-261. (ApJ Homepage)
Publication Date:
03/2008
Origin:
UCP
ApJ Keywords:
Cosmology: Dark Matter, Galaxies: Halos, Cosmology: Large-Scale Structure of Universe, Methods: Statistical
DOI:
10.1086/528954
Bibliographic Code:
2008ApJ...676..248Y

Abstract

We investigate various galaxy occupation statistics of dark matter halos using a large galaxy group catalog constructed from the Sloan Digital Sky Survey Data Release 4 (SDSS DR4) with an adaptive halo-based group finder. The conditional luminosity function (CLF) is measured separately for all, red, and blue galaxies, as well as in terms of central and satellite galaxies. The CLFs for central and satellite galaxies can be well modeled with a lognormal distribution and a modified Schechter form, respectively. About 85% of the central galaxies and about 80% of the satellite galaxies in halos with masses Mh>~1014 h-1 Msolar are red galaxies. These numbers decrease to 50% and 40%, respectively, in halos with Mh~1012 h-1 Msolar. For halos of a given mass, the distribution of the luminosities of central galaxies, Lc, has a dispersion of about 0.15 dex. The mean luminosity (stellar mass) of the central galaxies scales with halo mass as Lc~M0.17h (M*,c~M0.22h) for halos with masses M>>1012.5 h-1 Msolar, and both relations are significantly steeper for less massive halos. We also measure the luminosity and stellar mass gaps between the first and second brightest (most massive) member galaxies, logL1-logL2 (logM*,1-logM*,2). These gap statistics, especially in halos with Mh<~1014.0 h-1 Msolar, indicate that the luminosities of central galaxies are clearly distinct from those of their satellites. The fraction of fossil groups, defined as those groups with logL1-logL2>=0.8, ranges from ~2.5% for groups with Mh~1014 h-1 Msolar to 18%-60% for groups with Mh~1013 h-1 Msolar. Finally, we measure the fraction of satellites, which changes from ~5.0% for galaxies with 0.1Mr-5logh~-22.0 to ~40% for galaxies with 0.1Mr-5logh~-17.0.

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