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The spatial clustering of X-ray selected AGN in the XMM-COSMOS field

Gilli, R. and Zamorani, G. and Miyaji, T. and Silverman, J. and Brusa, M. and Mainieri, V. and Cappelluti, N. and Daddi, E. and Porciani, C. and Pozzetti, L. and Civano, F. and Comastri, A. and Finoguenov, A. and Fiore, F. and Salvato, M. and Vignali, C. and Hasinger, G. and Lilly, S. and Impey, C. and Trump, J. and Capak, P. and McCracken, H. and Scoville, N. and Taniguchi, Y. and Carollo, C. M. and Contini, T. and Kneib, J.-P. and Le Fevre, O. and Renzini, A. and Scodeggio, M. and Bardelli, S. and Bolzonella, M. and Bongiorno, A. and Caputi, K. and Cimatti, A. and Coppa, G. and Cucciati, O. and de la Torre, S. and de Ravel, L. and Franzetti, P. and Garilli, B. and Iovino, A. and Kampczyk, P. and Knobel, C. and Kovač, K. and Lamareille, F. and Le Borgne, J.-F. and Le Brun, V. and Maier, C. and Mignoli, M. and Pellò, R. and Peng, Y. and Perez Montero, E. and Ricciardelli, E. and Tanaka, M. and Tasca, L. and Tresse, L. and Vergani, D. and Zucca, E. and Abbas, U. and Bottini, D. and Cappi, A. and Cassata, P. and Fumana, M. and Guzzo, L. and Leauthaud, A. and Maccagni, D. and Marinoni, C. and Memeo, P. and Meneux, B. and Oesch, P. and Scaramella, R. and Walcher, J. (2009) The spatial clustering of X-ray selected AGN in the XMM-COSMOS field. Astronomy and Astrophysics, 494 (1). pp. 33-48. ISSN 0004-6361.

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We study the spatial clustering of 538 X-ray selected AGN in the 2 deg^2 XMM-COSMOS field that are spectroscopically identified with I_(AB) < 23 and span the redshift range z = 0.2−3.0. The median redshift and X-ray luminosity of the sample are z = 0.98 and L_(0.5−10) = 6.3 × 10^43 erg s^−1, respectively. A strong clustering signal is detected at ∼18σ level, which is the most significant measurement obtained to date for clustering of X-ray selected AGN. By fitting the projected correlation function w(r_p) with a power law on scales of r_p = 0.3−40 h^−1 Mpc, we derive a best-fit comoving correlation length of r_0 = 8.6 ± 0.5 h^−1 Mpc and slope of γ = 1.88 ± 0.07 (Poissonian errors; bootstrap errors are about a factor of 2 larger). An excess signal is observed in the range r_p ∼ 5−15 h^−1 Mpc, which is due to a large-scale structure at z ∼ 0.36 containing about 40 AGN, a feature which is evident over many wavelengths in the COSMOS field. When removing the z ∼ 0.36 structure or computing w(rp) in a narrower range around the peak of the redshift distribution (e.g. z = 0.4−1.6), the correlation length decreases to r¬_0 ∼ 5−6 h^−1 Mpc, which is consistent with what is observed for bright optical QSOs at the same redshift. We investigate the clustering properties of obscured and unobscured AGN separately, adopting different definitions for the source obscuration. For the first time, we are able to provide a significant measurement for the spatial clustering of obscured AGN at z ∼ 1. Within the statistical uncertainties, we do not find evidence that AGN with broad optical lines (BLAGN) cluster differently from AGN without broad optical lines (non- BLAGN). Based on these results, which are limited by object statistics, however, obscured and unobscured AGN are consistent with inhabiting similar environments. The evolution of AGN clustering with redshift is also investigated. No significant difference is found between the clustering properties of XMM-COSMOS AGN at redshifts below or above z = 1. The correlation length measured for XMM-COSMOS AGN at z ∼ 1 is similar to that of massive galaxies (stellar mass M* ≳ 3 × 10^10 M⊙) at the same redshift. This suggests that AGN at z ∼ 1 are preferentially hosted by massive galaxies, as observed both in the local and in the distant (z ∼ 2) Universe. According to a simple clustering evolution scenario, we find that the relics of AGN are expected to have a correlation length as large as r_0 ∼ 8 h^−1 Mpc by z = 0, and hence to be hosted by local bright (L ∼ L*) ellipticals. We make use of dark matter halo catalogs from the Millennium simulation to determine the typical halo hosting moderately luminous z ∼ 1 AGN. We find that XMM-COSMOS AGN live in halos with masses M ≳ 2.5 × 10^12 M⊙h^−1. By combining the number density of XMM-COSMOS AGN to that of the hosting dark matter halos we estimate the AGN duty cycle and lifetimes. We find lifetimes approximately of 1 Gyr for AGN at z ∼ 1, which are longer than those estimated for optically bright QSOs at the same redshift. These longer lifetimes mainly reflect the higher number density of AGN selected by X-ray samples.

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Additional Information:© ESO 2009. Received 18 August 2008 / Accepted 22 October 2008. his work is based on observations obtained with XMM-Newton, an ESA Science Mission with instruments and contributions directly funded by ESA Member States and the USA (NASA). We gratefully acknowledge the contribution of the entire COSMOS collaboration (http:// In Italy, the XMM-COSMOS projects is supported by ASI-INAF and PRIN/MIUR under grants I/023/05/00 and 2006- 02-5203. The zCOSMOS ESO Large Program Number 175.A-0839 is acknowledged. R.G. thanks Carlo Nipoti, Federico Marulli, Enzo Branchini, and Lauro Moscardini for stimulating discussions. The referee is acknowledged for providing useful comments. The Millennium Simulation databases used in this paper and the web application providing online access to them were constructed as part of the activities of the German Astrophysical Virtual Observatory.
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Subject Keywords:galaxies: active; cosmology: large-scale structure of Universe; cosmology: observations; X-rays: galaxies
Record Number:CaltechAUTHORS:20090810-142635312
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Official Citation:The spatial clustering of X-ray selected AGN in the XMM-COSMOS field R. Gilli, G. Zamorani, T. Miyaji, J. Silverman, M. Brusa, V. Mainieri, N. Cappelluti, E. Daddi, C. Porciani, L. Pozzetti, F. Civano, A. Comastri, A. Finoguenov, F. Fiore, M. Salvato, C. Vignali, G. Hasinger, S. Lilly, C. Impey, J. Trump, P. Capak, H. McCracken, N. Scoville, Y. Taniguchi, C. M. Carollo, T. Contini, J.-P. Kneib, O. Le Fevre, A. Renzini, M. Scodeggio, S. Bardelli, M. Bolzonella, A. Bongiorno, K. Caputi, A. Cimatti, G. Coppa, O. Cucciati, S. de la Torre, L. de Ravel, P. Franzetti, B. Garilli, A. Iovino, P. Kampczyk, C. Knobel, K. Kova, F. Lamareille, J.-F. Le Borgne, V. Le Brun, C. Maier, M. Mignoli, R. Pellò, Y. Peng, E. Perez Montero, E. Ricciardelli, M. Tanaka, L. Tasca, L. Tresse, D. Vergani, E. Zucca, U. Abbas, D. Bottini, A. Cappi, P. Cassata, M. Fumana, L. Guzzo, A. Leauthaud, D. Maccagni, C. Marinoni, P. Memeo, B. Meneux, P. Oesch, R. Scaramella and J. Walcher A&A 494 (1) 33-48 (2009) DOI: 10.1051/0004-6361:200810821
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:14930
Deposited By: Tony Diaz
Deposited On:03 Sep 2009 17:37
Last Modified:06 Jul 2015 20:52

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