The Spatial Distribution and Kinematics of Stellar Populations in E+A Galaxies

Abstract

We use long-slit spectroscopic observations of the sample of E+A galaxies described by Zabludoff et al. to constrain the nature of the progenitors and remnants of the E+A phase of galaxy evolution. We measure spatially resolved kinematic properties of the young (1 Gyr) and old (few Gyr) stellar populations. The young stellar populations are more centrally concentrated than the older populations, but they are not confined to the galaxy core (radius 1 kpc). The kinematics of the old stellar population place 16 of 20 of our E+As on a trend parallel to the Faber-Jackson relation that is offset by ~0.6 mag in R. Eighteen of 20 E+As have v/σ < 1. As the young stars in these systems evolve, the luminosity offset will disappear, and the remnants will be pressure-supported systems that lie on the Faber-Jackson relation. Although Zabludoff et al. spectroscopically selected the most extreme E+A galaxies in the local volume, the sample is kinematically diverse: velocity dispersions range from 30 km s-1 to ~200 km s-1 over a luminosity range of MR = -19 to -22 + 5 log h. Combining these results with an estimate of the number of galaxies that experience an E+A phase, we conclude that the E+A phase of galaxy evolution is important in the development of a large fraction of spheroid-dominated galaxies over a wide range of luminosities and masses. Our kinematic observations, together with evidence that E+As have recently evolved from a vigorous star-forming phase to a quiescent phase (e.g., Couch & Sharples; Caldwell et al.) and that many have tidal features consistent with disklike progenitors (Zabludoff et al.), indicate that these galaxies are undergoing a transformation from gas-rich, star-forming, rotationally supported, disk-dominated galaxies into gas-poor, quiescent, pressure-supported, spheroid-dominated galaxies.