10983(  1) - 04/03/06 11:22  - [  1]

                  HUBBLE SPACE TELESCOPE OBSERVING PROGRAM 10983

Version: 1    Check-in Time: 03-Apr-2006 15:22:04

Title
Galaxy Bulges in Clusters: formation and evolution to z ~ 1
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Type             Cycle     Parallel Pointing Tolerance
AR               15        <none>
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Investigators
                                                                                     Contact?
    PI: Dr. Yogesh Wadadekar              Space Telescope Science Institute
   CoI: Dr. Stefano Casertano             Space Telescope Science Institute             N
   CoI: Prof. Ajit Kembhavi               Inter-University Centre for Astronomy and     N
                                          Astrophysics
   CoI: Mr. Abhishek Rawat                Inter-University Centre for Astronomy and     N
                                          Astrophysics

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Abstract

The likely existence of two fundamentally distinct classes of galactic bulges - old,
metal-enriched, and following a R^1/4 profile, vs. young, exponential, and possibly
less metal-enriched - has recently emerged as a very important clue to the formation
history of nearby galaxies of different Hubble types and luminosities. We propose to
take advantage of archival HST data to extend the study of the duality in bulge
properties beyond the local Universe, specifically to a sample of about 40 galaxy
clusters at 0.2 < z < 0.9 with deep WFPC2 or ACS observations. Understanding how -
and when - bulges and ellipticals formed in clusters, and how their properties
relate to those of galaxies in the local Universe, will help answer fundamental
questions about galaxy formation in clusters and in the field. If exponential bulges
form through secular evolution, they should be rarer and fainter at higher
redshifts; if R^1/4 bulges form in burst at high redshift, their number, size, and
color should evolve accordingly. We will address this question by quantitatively
estimating structural parameters for the bulge and disk using analytic 2-D fits to
the galaxy images using a bulge-disk decomposition code independently developed by
the PI. We expect to obtain these measurements for about 1000 bulges and ellipticals
to I=23 in about 40 available clusters with deep high resolution HST observations.
We will also be able to understand the impact on bulge evolution of mergers, through
the incidence of disturbed morphologies, and of the local environment, via
correlations with cluster richness and position within the cluster. A companion
project, recently started by two co-investigators (and for which no funding is
requested), will address similar questions for field galaxies in the GOODS survey.
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