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F. Menanteau, H. C. Ford, A. R. Martel (Johns Hopkins University), ACS Science Team
We investigate the internal color properties of a sample of ~85 (i775 < 25.5) morphologically selected spheroid galaxies in the Hubble Ultra Deep Field. The unprecedented deep multicolor BViz information enables us to study in great detail the resolved galaxy colors. We augment our database of spectroscopic redshifts with Bayesian photometric estimates from the BViz and NICMOS J and H bands in order to examine the redshift evolution in the spheroids' internal color structure between 0.4 < z < 1.4. As in previous studies, we find that a significant fraction of spheroids show perturbed internal colors which in many cases manifest themselves by presence of central blue clumps. We correlate our sample with Chandra archival information and find that the three spheroids with X-ray counterparts display blue cores. These account for ~ 10% of the spheroids with strong internal color variations in which blue light can be attributed to nuclear activity. We use stellar synthesis models and maximum likelihood to obtain pixel-to-pixel K-corrections and SFR estimates from the models. Using the fits we compute the rest-frame color variations of spheroids and investigate its relation with their asymmetry and luminosity. Finally, we compare our sample with the internal properties of a sample of cluster ellipticals at z ~0.8 from the ACS/GTO intermediate clusters survey.
ACS was developed under NASA contract NAS 5-32865, and this research is supported by NASA grant NAG5-7697.
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Bulletin of the American Astronomical Society, 37 #4
© 2005. The American Astronomical Soceity.