Title:   

       Color Gradients in Elliptical Galaxies: Evidence for
       Environmental Dependence of Galaxy Formation Process ?

Naoyuki Tamura
University of Durham, U.K.

Abstract:

Nearby elliptical galaxies are known to have radial gradients of color
and metal absorption line strength; colors gradually become redder and
metal absorption lines become stronger towards the center, suggesting
that stellar population in an elliptical galaxy changes with radius.
Such a radial gradient of stellar population is likely to be a
powerful probe of how the galaxy formed. On the other hand, formation
history of elliptical galaxy is likely to depend on its environment.
Therefore, it is important to study the observational properties in
various environments and compare one population with another.

Radial gradients of color and metal absorption line strength gradient
have been investigated so far in several tens of nearby elliptical
galaxies. One of the shortcomings of these studies, however, is that
almost all the galaxies reside not in rich clusters but in relatively
sparse environments. Recently, we performed B and R band surface
photometry for E/S0 galaxies in rich clusters (ABELL 2199 and Coma).
Based on the results from our data and those from the literature, I
will discuss formation process of elliptical galaxy and its
environmental dependence.