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arXiv · 1104.2904

AGN environments at z<1.5 in the UKIDSS Ultra-Deep Survey

E. J. Bradshaw·O. Almaini·W. G. Hartley·R. W. Chuter·C. Simpson·C. J. Conselice·J. S. Dunlop·R. J. McLure·M. Cirasuolo
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Abstract

We investigate the environments of both X-ray and radio-loud AGN within the UKIDSS Ultra-deep Survey (UDS) using deep infrared selection to sample the galaxy density field in the redshift range 1.0 <= z <= 1.5. Using angular cross-correlation techniques we find that both X-ray and radio-loud AGN preferentially reside in overdense environments. We also find that both types of AGN cluster more strongly with those galaxies classified as `passive' rather than those that are actively star-forming. We infer clustering scale lengths comparable to those of passive red galaxies, suggesting that typical AGN at these epochs reside in dark-matter halos of mass M >~ 10^13 M_sun. A closer look at the small-scale environments of the AGN reveals that the neighbouring galaxies of radio-loud AGN have U-B colours more skewed towards the `green-valley' and the red sequence, whereas the neighbours of X-ray AGN show no difference to the general galaxy population. This suggests that although both AGN types live in overdense environments, the radio-loud AGN may be preferentially located in more evolved cluster cores, in a similar environment to low-powered radio AGN in the local Universe.

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E. J. Bradshaw, O. Almaini, W. G. Hartley, R. W. Chuter, C. Simpson, C. J. Conselice, J. S. Dunlop, R. J. McLure, M. Cirasuolo. 2011-04-18. AGN environments at z<1.5 in the UKIDSS Ultra-Deep Survey. https://doi.org/10.1111/j.1365-2966.2011.18888.x

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