Tracing the nuclear accretion history of the red galaxy population

Kate Brand, Arjun Dey, Michael J.I. Brown, Casey R. Watson, Buell T. Jannuzi, Joan R. Najita, Christopher S. Kochanek, Joseph C. Shields, Giovanni G. Fazio, William R. Forman, Paul J. Green, Christine J. Jones, Almus T. Kenter, Brian R. McNamara, Steve S. Murray, Marcia Rieke, Alexey Vikhlinin

Research output: Contribution to journalArticlepeer-review

23 Scopus citations


We investigate the evolution of the hard X-ray luminosity of the red galaxy population using a large sample of 3316 red galaxies selected over a wide range in redshift (0.3 < z < 0.9) from a 1.4 deg2 region in the Boǒ̈tes field of the NOAO Deep Wide-Field Survey (NDWFS). The red galaxies are early-type, bulge-dominated galaxies and are selected to have the same evolution-corrected, absolute A-band magnitude distribution as a function of redshift to ensure that we are tracing the evolution in the X-ray properties of a comparable optical population. Using a stacking analysis of 5 ks Chandra/ACIS observations within this field to study the X-ray emission from these red galaxies in three redshift bins, we find that the mean X-ray luminosity increases as a function of redshift. The large mean X-ray luminosity and the hardness of the mean X-ray spectrum suggest that the X-ray emission is largely dominated by active galactic nuclei (AGNs) rather than stellar sources. The hardness ratio can be reproduced by either an absorbed (NH ≈ 2 × 1022 cm-2) Γ = 1.7 power-law source, consistent with that of a population of moderately obscured Seyfert-like AGNs, or an unabsorbed Γ = 0.7 source, suggesting a radiatively inefficient accretion flow (e.g., an advection-dominated accretion flow). We also find that the emission from this sample of red galaxies constitutes at least 5% of the hard X-ray background. These results suggest a global decline in the mean AGN activity of normal early-type galaxies from z ∼ 1 to the present, which indicates that we are witnessing the tailing off of the accretion activity onto supermassive black holes in early-type galaxies since the quasar epoch.

Original languageEnglish (US)
Pages (from-to)723-732
Number of pages10
JournalAstrophysical Journal
Issue number2 I
StatePublished - Jun 20 2005


  • Cosmology: observations
  • Galaxies: active
  • Galaxies: elliptical and lenticular, cD
  • Galaxies: evolution

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science


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