Title:  
         The Environmental Effects on Cluster Galaxy Evolution Based 
         on the SDSS Data


Tomotsugu Goto
Carnegie Mellon University, and 
University of Tokyo




Abstract:
 
We constructed a galaxy cluster catalog with the Sloan Digital Sky Survey (SDSS) 
data using a newly developed, non-parametric cluster finder; Cut & Enhance method.
The cluster photometric redshift estimation is accurate with dz=+-0.015 at z<0.3.
The composite luminosity functions of these clusters show that cluster galaxies 
have brighter M* and flatter faint-end-tail compared with the field LF. Among
cluster galaxies, elliptical galaxies are shown to have flatter faint end tail 
than spiral galaxies. For richer 514 clusters, we study a fraction of blue
galaxies as a function of redshift (the Butcher-Oemler effect). In both g-r and 
u-r colors, the blue galaxy fraction is found to increase with increasing redshift
(0<z<0.3). We further study a fraction of spiral galaxies using concentration and
profile fits as a morphological indicator. It is found that morphologically spiral
galaxies in fact increase as a function of redshift, just like a morphological
equivalent of the Butcher-Oemler effect.  To investigate the properties of galaxies 
in more detail, we studied nearby galaxies with the SDSS spectroscopy (0.05<z<0.1). 
We found that Hdelta is strong (post-starburst) galaxies, which have been claimed 
to be cluster related, do not live preferentially in cluster region.  On the other 
hand, passive spiral galaxies --- a weird population of galaxies with spiral arms 
and no star fromation --- live in the cluster infalling regions.  We also studied 
the morphology-density relation using the automated morphological classification 
and found that there are two characteristic environment where galaxy population 
changes, suggesting possible existence of two physical mechanisms govering cluster 
galaxy evolution.