Gemini Deep Deep Survey VI: Massive post-starburst galaxies at z=1

Authors:
  • DBDamien Le Borgne
    Damien Le Borgne
  • RARoberto Abraham
    Roberto Abraham
  • KDKathryne Daniel
    Kathryne Daniel
  • PMPatrick McCarthy
    Patrick McCarthy
  • KGKarl Glazebrook
    Karl Glazebrook
  • SSSandra Savaglio
    Sandra Savaglio
  • DCDavid Crampton
    David Crampton
  • SJStephanie Juneau
    Stephanie Juneau
  • RCRay Carlberg
    Ray Carlberg
  • HCHsiao-Wen Chen
    Hsiao-Wen Chen
  • RMRonald O. Marzke
    Ronald O. Marzke
  • KRKathy Roth
    Kathy Roth
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Abstract
We show that there has been a dramatic decline in the abundance of massive post-starburst galaxies from z=1.2 to the present. Combining data from the Gemini Deep Deep and the Sloan Digital Sky Surveys to make mass-matched samples (M*>=10^10.2 Msun), we find that the fraction of galaxies in a post-starburst phase, identified by their strong Hdelta absorption lines, has decreased from about 50% at z=1.2 to a few percent today. This trend originates from a (1+z)^{2.5 \pm 0.7} evolution in the distribution of Hdelta equivalent widths for massive galaxies. With few exceptions, the local and the distant massive post-starburst galaxies have high visual extinction and young luminosity-weighted ages. Spectral synthesis studies of the high-redshift population using the PEGASE code, treating HdeltaA, EW[OII], Dn4000, and rest-frame colors, favor models in which these massive Hdelta-strong systems reveal the echoes of intense episodes of star-formation that faded ~1 Gyr prior to the epoch of observation on time-scales shorter than a few hundred million years. The z=1.4-2 epoch appears to be a time at which massive galaxies transition from a mode of sustained star formation to a quiet mode with weak and rare star-formation episodes. We argue that the most likely local counterparts for the distant massive post-starburst galaxies are passively evolving massive galaxies in the field and small groups.