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 $\sim$ 0.6 mag in R. Eighteen of 20 E+As have v/sigma < 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 to ~ 200 km/s over a luminosity range of M_R = -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 and Sharples, Caldwell et al.) and that many have tidal features consistent with disk-like progenitors (Zabludoff et al.), indicate that these galaxies are undergoing a transformation from star-forming, disk-dominated galaxies into quiescent, spheroid-dominated galaxies.