AAS Meeting #194 - Chicago, Illinois, May/June 1999
Session 4. Evolution of Galaxies, Galaxy Surveys
Display, Monday, May 31, 1999, 9:20am-6:30pm, Southwest Exhibit Hall

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[4.05] Evolution of Spheroidal Galaxies at z < 1.1 from DEEP Survey

M. Im (UCO/Lick Observatory), DEEP Team

The Deep Extragalactic Evolutionary Probe (DEEP) is currently a multi-year survey of faint, distant, field galaxies using the Keck 10-m telescope and the Hubble Space Telescope (HST). We have obtained spectra of almost 1000 faint galaxies so far, and our completeness level is 1.5-2 magnitudes fainter than that of surveys done by 4-m class telescopes. More importantly, our data provide unique information on mass for these faint galaxies from velocity width or rotation curve measurements, which have been lacking from other faint field galaxy surveys. With a subset of these data, we have the first statistically meaningful sample of spectroscopically confirmed red spheroidal galaxies in field at z ~0.8-1.1, selected by various methods from the corresponding HST images. Preliminary results show that i) colors of massive elliptical galaxies (L > L*) at z < 1.1 are consistent with predictions based upon pure passive evolution scenario with an initial star formation epoch at redshifts beyond 1, ii) the number density of massive elliptical galaxies has not increased significantly since z ~1. We also find blue spheroidal galaxies in our sample, but they all appear to be low mass systems, some possibly the moderate redshift progenitors of present day dwarf spheroidals. Our findings imply that, like elliptical galaxies in clusters, and contrary to previous observational and theoretical claims for rapid evolution of field ellipticals, massive elliptical galaxies in the field were already in place at z ~1 and have not evolved significantly since then, except for the expected luminosity fading of old stellar populations. Thus field ellipticals may yet provide a viable study of cosmological parameters of the universe with the redshift-volume test.

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