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Session 30 - Galaxy Evolution I.
Oral session, Monday, January 15
1st Floor, La Villita Assembly Building

[30.01] The Evolution of Early Type Galaxies at z > 1

Near-IR selection is ideal for the study of distant galaxy evolution because it minimizes bias toward finding strongly evolving or star forming galaxies. We have just completed a large area (100 arcmin^2) deep near--IR survey detecting galaxies to K\approx 22, J\approx 24 along with deep optical B,R and I images. We have estimated ``photometric redshifts'' for a sample of galaxies with accurate photometry and K<20 to identify the progenitors of early type galaxies at z > 1 by searching for objects with very red colors. In the K< 20 sample the median redshift is about 1.3 with a tail extending to redshift 3 as is predicted by passively evolving galaxy models. A particulary interesting indicator of z > 1.5 galaxies is the J-K color which should be greater than 2. We find about 3 such galaxies per arcminute, which is similar to the total number of early type (E,S0 and Sa) L galaxies expected between 1 1 it would appear that most early type galaxies are already well formed by a redshift greater than 2 but that they do have a substantial UV excess at z > 1.5. Indeed, at redshifts in excess of 1.5 there are no galaxies redder than the colors of a current day Sab galaxy. Since our sample is K band selected there should be no bias against finding more weakly evolved early type galaxies and our survey area is large enough that we should have seen several hundred galaxies redder than Sab at z > 1. Thus, we are seeing strong color evolution in the population of early type galaxies.

Program listing for Monday