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Session 30 - Galaxy Evolution I.
Oral session, Monday, January 15
1st Floor, La Villita Assembly Building
I present results of an ongoing investigation of star formation evolution in early type (elliptical and bulge-dominated) field galaxies as a function of cosmic time. Such an investigation requires classifications, redshifts and differential colors for a large sample of objects; this information is being extracted from a six-color optical deep-sky survey, obtained with the 4-meter telescope at Kitt Peak. The dataset covers 0.83 square degree of sky, with U-B-V-R-I(7500ÅI(8600Åphotometry complete to M_R\sim23, and contains some 9000 cataloged galaxies, of which 7000 have data in at least three colors.
I have developed a technique to identify both the spectral type and redshift of the survey field galaxies using the multiband color data. Using model colors and spectral energy distributions of typical E/S0, Sbc, Scd and Irr galaxies, the spectroscopic Hubble type of each galaxy can be determined, along with its redshift to \Delta z \pm 0.06 for late-type galaxies and \pm 0.03 for early-type galaxies. This has been confirmed with spectroscopic observations of sample galaxies, and with photometric observations of galaxies with previously published redshifts using the survey's filter system. Comparison of the rest-frame blue and near-UV colors of the early-type galaxies at different epochs quantifies their star formation evolution as functions of both redshift and luminosity.
