Volume 445, Number 1, January I 2006
|Page(s)||29 - 42|
|Section||Cosmology (including clusters of galaxies)|
|Published online||13 December 2005|
RASS-SDSS Galaxy cluster survey
IV. A ubiquitous dwarf galaxy population in clusters
Max-Planck-Institut fur extraterrestrische Physik, 85748 Garching, Germany e-mail: email@example.com
2 INAF – Osservatorio Astronomico di Trieste, via G. B. Tiepolo 11, 34131, Trieste, Italy
3 European Southern Observatory, Karl Scharzschild Strasse 2, 85748, Germany
Accepted: 8 June 2005
We analyze the Luminosity Functions (LFs) of a subsample of 69 clusters from the RASS-SDSS galaxy cluster catalog. When calculated within the cluster physical sizes, given by r200 or r500, all the cluster LFs appear to have the same shape, well fitted by a composite of two Schechter functions with a marked upturn and a steepening at the faint-end. Previously reported cluster-to-cluster variations of the LF faint-end slope are due to the use of a metric cluster aperture for computing the LF of clusters of different masses. We determine the composite LF for early- and late-type galaxies, where the typing is based on the galaxy colors. The late-type LF is well fitted by a single Schechter function with a steep slope ( in the r band, within r200). The early-type LF instead cannot be fitted by a single Schechter function, and a composite of two Schechter functions is needed. The faint-end upturn of the global cluster LF is due to the early-type cluster galaxies. The shape of the bright-end tail of the early-type LF does not seem to depend upon the local galaxy density or the distance from the cluster center. The late-type LF shows a significant variation only very near the cluster center. On the other hand, the faint-end tail of the early-type LF shows a significant and continuous variation with the environment. We provide evidence that the process responsible for creating the excess population of dwarf early type galaxies in clusters is a threshold process that occurs when the density exceeds ∼500 times the critical density of the Universe. We interpret our results in the context of the “harassment” scenario, where faint early-type cluster galaxies are predicted to be the descendants of tidally-stripped late-type galaxies.
Key words: galaxies: clusters: general / galaxies: luminosity function, mass function
© ESO, 2005
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