Field E+A Galaxies at Intermediate Redshifts (0.3 < z < 1)

Abstract

We select E+A candidates from a spectroscopic data set of ~800 field galaxies and measure the E+A fraction at 0.3<z<1 to be 2.7%+/-1.1%, a value lower than that in galaxy clusters at comparable redshifts (11%+/-3%). HST WFPC2 imaging for five of our six E+A's shows that they have a heterogeneous parent population: these E+A's span a range in half-light radius (0.8h^-1kpc<r_1/2<8h^-1kpc) and estimated internal velocity dispersion (50kms^-1<~σ_est<~220kms^-1), and they include luminous systems (-21.6<=M_Bz-5logh<=-19.2). Despite their diversity in some aspects, the E+A's share several common characteristics that indicate that the E+A phase is an important link in the evolution of star-forming galaxies into passive systems: the E+A's are uniformly redder than the blue, star-forming galaxies that make up the majority of the field, they are more likely to be bulge-dominated than the average field galaxy, and they tend to be morphologically irregular. We find that E+A's make up ~9% of the absorption-line systems in this redshift range and estimate that >~25% of passive galaxies in the local field had an E+A phase at z<~1.

Based on observations with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy (AURA), Inc., under NASA contract NAS 5-26555.

Based on observations obtained at the W. M. Keck Observatory, which is operated jointly by the California Institute of Technology and the University of California.