AEGIS: The Color-Magnitude Relation for X-Ray-selected Active Galactic Nuclei

We discuss the relationship between rest-frame color and optical luminosity for X-ray sources in the range 0.6< z <1.4 selected from the Chandra survey of the Extended Groth Strip. These objects are almost exclusively active galactic nuclei (AGNs). While there are a few luminous QSOs, most are...

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Bibliographic Details
Published in:The Astrophysical journal Vol. 660; no. 1; pp. L11 - L14
Main Authors: Nandra, K, Georgakakis, A, Willmer, C. N. A, Cooper, M. C, Croton, D. J, Davis, M, Faber, S. M, Koo, D. C, Laird, E. S, Newman, J. A
Format: Journal Article
Language:English
Published: IOP Publishing 01.05.2007
ISSN:1538-4357, 0004-637X, 1538-4357
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Summary:We discuss the relationship between rest-frame color and optical luminosity for X-ray sources in the range 0.6< z <1.4 selected from the Chandra survey of the Extended Groth Strip. These objects are almost exclusively active galactic nuclei (AGNs). While there are a few luminous QSOs, most are relatively weak or obscured AGNs whose optical colors should be dominated by host galaxy light The vast majority of AGN hosts at z 6 1 are luminous and red, with very few objects fainter than M sub(B) = -20.5 or bluer than U-B = 0.6. This places the AGNs in a distinct region of color-magnitude space, on the "red sequence" or at the top of the "blue cloud," with many in between these two modes in galaxy color. A key stage in the evolution of massive galaxies is when star formation is quenched, resulting in a migration from the blue cloud to the red sequence. Our results are consistent with scenarios in which AGNs either cause or maintain this quenching. The large number of red-sequence AGNs implies that strong, ongoing star formation is not a necessary ingredient for AGN activity, as black hole accretion appears often to persist after star formation has been terminated.
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ISSN:1538-4357
0004-637X
1538-4357
DOI:10.1086/517918