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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

Silverman, J.D., Mainieri, V., Lehmer, B.D., Alexander, D.M., Bauer, F.E., Bergeron, J., Brandt, W.N., Gilli, R., Hasinger, G., Schneider, D.P., Tozzi, P., Vignali, C., Koekemoer, A.M., Miyaji, T., Popesso, P., Rosati, P. & Szokoly, G. (2008). The evolution of AGN host galaxies from blue to red and the influence of large-scale structures. The astrophysical journal 675(2): 1025-1040.

Author(s) from Durham


We present an analysis of 109 moderate-luminosity (41.9<=logL0.5-8.0keV<=43.7) AGNs in the Extended Chandra Deep Field-South survey, which is drawn from 5549 galaxies from the COMBO-17 and GEMS surveys having 0.4<=z<=1.1. These obscured or optically weak AGNs facilitate the study of their host galaxies since the AGNs provide an insubstantial amount of contamination to the galaxy light. We find that the color distribution of AGN host galaxies is highly dependent on (1) the strong color-evolution of luminous (MV<-20.7) galaxies, and (2) the influence of ~10 Mpc scale structures. When excluding galaxies within the redshift range 0.63<=z<=0.76, a regime dominated by sources in large-scale structures at z=0.67 and z=0.73, we observe a bimodality in the host galaxy colors. Galaxies hosting AGNs at z>~0.8 preferentially have bluer (rest-frame U-V<0.7) colors than their z<~0.6 counterparts (many of which fall along the red sequence). The fraction of galaxies hosting AGNs peaks in the ``green valley'' (0.52.5) galaxies have the highest fraction of AGN (21%) in our sample. We explore the scenario that the evolution of AGN hosts is driven by galaxy mergers and illustrate that an accurate assessment requires a larger area survey since only three hosts may be undergoing a merger with timescales <~1 Gyr following a starburst phase.