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All-wavelength Extended Groth strip International Survey: the environment of X-ray sources at z~1

A. Georgakakis·K. Nandra·E. S. Laird·M. C. Cooper·B. F. Gerke·J. A. Newman·D. J. Croton·M. Davis·S. M. Faber·A. L. Coil
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Abstract

We explore the environment of z~1 AGN using a sample of 53 spectroscopically identified X-ray sources in the All-wavelength Extended Groth strip International Survey. We quantify the local density in the vicinity of an X-ray source by measuring the projected surface density of spectroscopically identified optical galaxies within a radius defined by the 3rd nearest neighbour. Our main result is that X-ray selected AGN at z~1 avoid underdense regions at the 99.89% confidence level. Moreover, although we find that the overall population shares the same (rich) environment with optical galaxies of similar U-B and M_B, there is also tentative evidence (96%) that AGN with blue colors (U-B<1) reside in denser environments compared to optical galaxies. We argue that the results above are a consequence of the whereabouts of massive galaxies, capable of hosting supermassive black holes at their centers, with available cold gas reservoirs, the fuel for AGN activity. At z~1 an increasing fraction of such systems are found in dense regions.

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A. Georgakakis, K. Nandra, E. S. Laird, M. C. Cooper, B. F. Gerke, J. A. Newman, D. J. Croton, M. Davis, S. M. Faber, A. L. Coil. 2006-07-12. All-wavelength Extended Groth strip International Survey: the environment of X-ray sources at z~1. https://arxiv.org/abs/astro-ph/0607274

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