Spectroscopic Evolution of Dusty Starburst Galaxies in Distant Clusters

Abstract

By using a one-zone chemical and spectrophotometric evolution model of a disk galaxy undergoing a dusty starburst, we investigate numerically the optical spectroscopic properties in order to explore galaxy evolution in distant clusters. We adopt an assumption that the degree of dust extinction (represented by AV) depends on the ages of starburst populations in such a way that younger stars have larger AV (originally referred to as selective dust extinction by Poggianti & Wu). In particular, we investigate how the time evolution of the equivalent widths of [O II] lambda3727 and Hdelta are controlled by the adopted age dependence. This leads to the following three main results: (1) If a young stellar population (with an age of ~10^6 yr) is more heavily obscured by dust than an old one (>10^8 yr), the galaxy can show an ``e(a)'' spectrum characterized by strong Hdelta absorption and relatively modest [O II] emission. (2) A dusty starburst galaxy with an e(a) spectrum can evolve into a poststarburst galaxy with an a+k (or k+a) spectrum 0.2 Gyr after the starburst and then into a passive one with a k-type spectrum 1 Gyr after the starburst. This result clearly demonstrates an evolutionary link between galaxies with different spectral classes [i.e., e(b), e(a), a+k, k+a, and k]. (3) A dusty starburst galaxy can show an a+k or k+a spectrum even in the dusty starburst phase if the age-dependence of dust extinction is rather weak; i.e., if young starburst populations with different ages (