NOAO/KPNO-NSO,

DEPARTMENT OF ASTRONOMY AND

STEWARD OBSERVATORY AND NRAO

The University of Arizona

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JOINT COLLOQUIUM

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• Dr. Kim-Vy H. Tran

of the

• Institute for Astronomy, ETH Hoenggerberg Campus

who will present a talk entitled

• "Nature of E+A Galaxies in Intermediate Redshift Clusters"

Abstract: Combining HST/WFPC2 mosaics with extensive ground-based spectroscopy, we study the nature of E+A galaxies in three intermediate redshift clusters (z=0.33, 0.58, & 0.83). From a sample of ~500 confirmed cluster members, we isolate 46 E+A candidates to determine the E+A fraction and study their physical properties. We find E+A's comprise a non-negligible component (~7-13%) of the cluster population at these redshifts, and their diverse nature indicates a heterogeneous parent population. Cluster E+A's span the range in Hubble type and cover a wide range in luminosity, internal velocity dispersion, and half-light radius. From their velocity dispersions and half-light radii, we infer that the descendants of E+A's in our highest redshift cluster are massive early-type galaxies. We find a decrease in the characteristic E+A mass similar to the decrease in luminosity of rapidly star-forming field galaxies since z~1, i.e. galaxy "down-sizing." In addition, we argue our statistics imply that >30% of the E-S0 members have undergone an E+A phase; the true fraction could be 100% if the effects of E+A down-sizing, an increasing E+A fraction with redshift, and the conversion of spirals into early-types are also considered. Thus, the E+A phase may indeed be an important stage in the transformation of star-forming galaxies into early-type cluster members.

• on Thursday, December 18, 2003

• at 4:00 p.m.

• in Steward Observatory Lecture Hall--Room N210

Refreshments at 3:30PM in the Lobby