Computer Science
Scientific paper
Jul 2003
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2003hst..prop.9937k&link_type=abstract
HST Proposal ID #9937
Computer Science
Hst Proposal Id #9937 Cosmology
Scientific paper
The ages and age spread of spheroids remain important problems in galaxy evolution research. Both have been estimated for local galaxies via the color-magnitude relation {CMR}. To measure the CMR for distant galaxies, HST images are vital because of the high spatial resolution needed to separate the tiny {few 0.1"} bulges from disks and because of the high precision photometry needed to measure the dispersion in color of the spheroid subcomponent at the few % level. We have just completed a study of field spheroids near redshift z 0.8 from the Groth Strip, using V & I HST images and Keck redshifts. We find two surprising results: despite evidence for 1 mag or more of luminosity brightening, 1} the luminous spheroids show little change from present-day U-B colors and 2} their color dispersion is small. Due to uncertainties in the K-corrections, our results are valid only near z 0.8. We propose here to undertake a vastly improved study with the ACS data in the GOODS fields. The 4 filters will allow us to extend our analysis to lower and higher redshifts. The deeper ACS data will allow us a} to improve the photometry of galaxy subcomponents and estimates of the color dispersion, b} to measure lower luminosity spheroids, and c} to relax our assumptions on light profile shapes. Finally, the larger field of GOODS will enlarge the spheroid sample, thereby allowing searches for differences in age and age spread among subsamples divided by redshift, disk properties, bulge sizes, bulge ellipticities, etc. It should be noted that photometric redshifts are not adequate because of correlations between colors and derived redshifts. Thus the color dispersion work requires independent, precision redshifts that come from spectroscopy. These will be gathered from public redshift surveys in the GOODS fields.
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