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Higher prevalence of X-ray selected AGN in intermediate-age galaxies up to z similar to 1



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Pérez González, Pablo Guillermo and Cardiel López, Nicolás and Esquej Alonso, María del Pilar and Gallego Maestro, Jesús (2014) Higher prevalence of X-ray selected AGN in intermediate-age galaxies up to z similar to 1. Monthly notices of the Royal Astronomical Society, 443 (4). pp. 3538-3549. ISSN 0035-8711


Official URL: http://dx.doi.org/10.1093/mnras/stu1413


We analyse the stellar populations in the host galaxies of 53 X-ray selected optically dull active galactic nuclei (AGN) at 0.34 < z < 1.07 with ultradeep (m(AB) = 26.5, 3 sigma) optical medium-band (R similar to 50) photometry from the Survey for High-z Absorption Red and Dead Sources (SHARDS). The spectral resolution of SHARDS allows us to consistently measure the strength of the 4000 angstrom brk, D-n(4000), a reliable age indicator for stellar populations. We confirm that most X-ray selected moderate-luminosity AGN (L-X < 10(44) erg s(-1)) are hosted by massive galaxies (typically M-* > 10(10.5) M circle dot) and that the observed fraction of galaxies hosting an AGN increases with the stellar mass. A careful selection of random control samples of inactive galaxies allows us to remove the stellar mass and redshift dependences of the AGN fraction to explore trends with several stellar age indicators. We find no significant differences in the distribution of the rest-frame U - V colour for AGN hosts and inactive galaxies, in agreement with previous results. However, we find significantly shallower 4000 angstrom bres in AGN hosts, indicative of younger stellar populations. With the help of a model-independent determination of the extinction, we obtain extinction-corrected U - V colours and light-weighted average stellar ages. We find that AGN hosts have younger stellar populations and higher extinction compared to inactive galaxies with the same stellar mass and at the same redshift. We find a highly significant excess of AGN hosts with D-n(4000) similar to 1.4 and light-weighted average stellar ages of 300-500 Myr, as well as a deficit of AGN in intrinsic red galaxies. We interpret failure in recognizing these trends in previous studies as a consequence of the balancing effect in observed colours of the age-extinction degeneracy.

Item Type:Article
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This article has been accepted for publication in Monthly notices of the Royal Astronomical Society Journal © 2012 RAS. Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved. We thank the anonymous referee for their useful comments that helped to improve this paper. AH-C and AA-H acknowledge funding by the Universidad de Cantabria Augusto González Linares programme and the Spanish Plan Nacional de Astronomía y Astrofísica under grant AYA2012-31447. PE and PGP-G acknowledge support from the Spanish Plan Nacional grant AYA2012-31277. This work has made use of the Rainbow Cosmological Surveys Database, which is operated by the Universidad Complutense de Madrid (UCM), partnered with the University of California Observatories at Santa Cruz (UCO/Lick, UCSC). Based on observations made with the GTC, installed at the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofísica de Canarias, in the island of La Palma.

Uncontrolled Keywords:Active galactic nuclei; Supermassive black-holes; Ultraluminous infrared galaxies; Star-forming galaxies; Digital sky survey; Deep field-south; Host galaxies; Luminosity function; High-redshift; Stellar masses
Subjects:Sciences > Physics > Astrophysics
ID Code:29990
Deposited On:21 May 2015 08:37
Last Modified:10 Dec 2018 15:05

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