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AGN-host galaxy connection: morphology and colours of X-ray selected AGN at z ≤ 2

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Pović, M. and Sánchez Portal, M. and Pérez García, A. M. and Bongiovanni, A. and Cepa, J. and Huertas Company, M. and Lara López, M. A. and Fernández Lorenzo, M. and Ederoclite, A. and Alfaro, E. and Castañeda, H. and Gallego Maestro, Jesús and González Serrano, J. I. and González, J. J. (2012) AGN-host galaxy connection: morphology and colours of X-ray selected AGN at z ≤ 2. Astronomy and astrophysics, 541 . ISSN 0004-6361

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Official URL: http://dx.doi.org/10.1051/0004-6361/201117314




Abstract

Context. The connection between active galactic nuclei (AGN) and their host galaxies has been widely studied and found to be of great importance for providing answers to some fundamental questions related to AGN fuelling mechanisms, and both their formation and evolution. Aims. Using X-ray data and one of the deepest broad-band optical data sets available, we study how morphology and colours are related to X-ray properties for sources at redshifts z ≤ 2.0, using a sample of 262 AGN in the Subaru/XMM-Newton Deep Survey (SXDS). Methods. We performed our morphological classification using the galSVM code, which is a new method that is particularly suited to dealing with high-redshift sources. Colour-magnitude diagrams were studied in relationship to redshift, morphology, X-ray obscuration, and X-ray-to-optical flux ratio. We analysed the different regions in the colour-magnitude diagrams, and searched for correlations with the observed properties of AGN populations using models of their formation and evolution. Results. We confirm that a robust and reliable morphological classification of a general galaxy population at high redshift should be based on a multi-parametric approach. At least 50% of X-ray detected AGN at z <= 2.0 analysed in this work reside in spheroidal and bulge-dominated galaxies, while at least 18% have disk-dominated hosts. This suggests that different mechanisms may be responsible for triggering the nuclear activity. When analysing populations of X-ray detected AGN in both colour-magnitude and colour-stellar mass diagrams, the highest number of sources is found to reside in the green valley at redshifts ≃0.5-1.5. However, a larger number of low-luminosity AGN have been detected than in previous works owing to the substantial depth of the SXDS optical data. Whether AGN are hosted by early-or late-type galaxies, no clear relationship has been found with the optical colours (independently of redshift), as is typical of normal galaxies. Both early-and late-type AGN cover similar ranges of X-ray obscuration, for both unobscured and obscured sources. Conclusions. Our findings appear to confirm some previous suggestions that X-ray selected AGN residing in the green valley represent a transitional population, quenching star formation by means of different AGN feedback mechanisms and evolving to red-sequence galaxies. They might be hosted by similar sources (the majority of sources being late-type elliptical and lenticular galaxies, and early-type spirals) with similar stellar populations, which are triggered mainly by major and/or minor mergers, and in some cases by means of secular mechanism, as shown in previous numerical simulations. In the aforementioned transition we observe different phases of AGN activity, with some AGN being in the "QSO-mode" detected as compact, blue, and unobscured in X-rays, and with others passing through different phases before and after the "QSO-mode", being obscured and unobscured in X-rays, respectively.


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© ESO 2012. We thank the anonymous referee for a detailed analysis of the paper and constructive comments. We also thank Isabel Márquez Pérez, Josefa Masegosa Gallego, Jack Sulentic, and Ascensión del Olmo Orozco for long and very useful discussions. This work was supported by the Spanish Plan Nacional de Astronomía y Astrofísica under grant AYA2011-29517-C03-01. J.I.G.S. acknowledges financial support from the Spanish Ministry of Science and Innovation under project AYA2008-06311-C02-02. M. P. acknowledges Junta de Andalucía and Spanish Ministry of Science and Innovation through projects PO8-TIC-03531 and AYA2010-15169. We thank the SXDS, CDF-S, and COMBO-17 teams for making their data available to the astronomical community. We acknowledge support from the Faculty of the European Space Astronomy Centre (ESAC). We thank XMM-Newton Helpdesk for their helpful comments during the X-ray data reduction. This research has made use of software provided by the XMM-Newton Science Operations Centre and Chandra X-ray Center (CXC) in the application packages SAS and CIAO, respectively. IRAF is distributed by the National Optical Astronomy Observatory, which is operated by the Association of Universities for Research in Astronomy (AURA) under cooperative agreement with the National Science Foundation. This publication makes use of data products from the Two Micron All Sky Survey, which is a joint project of the University of Massachusetts and the Infrared Processing and Analysis Center California Institute of Technology, funded by the National Aeronautics and Space Administration and the National Science Foundation.

Uncontrolled Keywords:Active galactic nuclei; Supermassive black-holes; Deep field south; Degree extragalactic survey; Support vector machines; Hubble-space-telescope; Broad-band photometry; Seeing limited images; Photon imaging camera; XMM-Newton
Subjects:Sciences > Physics > Astrophysics
Sciences > Physics > Astronomy
ID Code:33628
Deposited On:20 Oct 2015 17:23
Last Modified:10 Dec 2018 15:05

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