Direct observational evidence for a large transient galaxy population in groups at 0.85 < z < 1 Academic Article uri icon

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  • (abridged) We introduce our survey of galaxy groups at 0.8515 members. The dynamical mass estimates are in good agreement with the masses estimated from the X-ray luminosity, with most of the groups having 131E10.1 Msun, and for blue galaxies we sample masses as low as Mstar=1E8.8 Msun. Like lower-redshift groups, these systems are dominated by red galaxies, at all stellar masses Mstar>1E10.1 Msun. Few group galaxies inhabit the "blue cloud" that dominates the surrounding field; instead, we find a large and possibly distinct population of galaxies with intermediate colours. The "green valley" that exists at low redshift is instead well-populated in these groups, containing ~30 per cent of galaxies. These do not appear to be exceptionally dusty galaxies, and about half show prominent Balmer-absorption lines. Furthermore, their HST morphologies appear to be intermediate between those of red-sequence and blue-cloud galaxies of the same stellar mass. We postulate that these are a transient population, migrating from the blue cloud to the red sequence, with a star formation rate that declines with an exponential timescale 0.6 Gyr< tau < 2 Gyr. Their prominence among the group galaxy population, and the marked lack of blue, star-forming galaxies, provides evidence that the group environment either directly reduces star formation in member galaxies, or at least prevents its rejuvenation during the normal cycle of galaxy evolution.


  • Balogh, Michael L
  • McGee, Sean L
  • Wilman, David J
  • Finoguenov, Alexis
  • Parker, Laura
  • Connelly, Jennifer L
  • Mulchaey, John S
  • Bower, Richard G
  • Tanaka, Masayuki
  • Giodini, Stefania

publication date

  • April 21, 2011