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Are Compton-Thick AGN the Missing Link Between Mergers and Black Hole Growth?

Kocevski, Dale D. and Brightman, Murray and Nandra, Kirpal and Koekemoer, Anton M. and Salvato, Mara and Aird, James and Bell, Eric F. and Hsu, Li-Ting and Kartaltepe, Jeyhan S. and Koo, David C. and Lotz, Jennifer M. and McIntosh, Daniel H. and Mozena, Mark and Rosario, David J. and Trump, Jonathan R. (2015) Are Compton-Thick AGN the Missing Link Between Mergers and Black Hole Growth? Astrophysical Journal, 814 (2). Art. No. 104. ISSN 0004-637X.

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We examine the host morphologies of heavily obscured active galactic nuclei (AGNs) at z ~ 1 to test whether obscured super-massive black hole growth at this epoch is preferentially linked to galaxy mergers. Our sample consists of 154 obscured AGNs with N_H > 10^(23.5) cm^(-2) and z 1.5. Using visual classifications, we compare the morphologies of these AGNs to control samples of moderately obscured 10^(22) cm^(-2) < N_H < 10^(23.5)cm^(-2) and unobscured (N_H < 10^(22) cm^(-2)) AGN. These control AGNs have similar redshifts and intrinsic X-ray luminosities to our heavily obscured AGN. We find that heavily obscured AGNs are twice as likely to be hosted by late-type galaxies relative to unobscured AGNs (65.3_(-4.6)^(+4.1)%) versus 34.5_(-2.7)^(+2.9)%) and three times as likely to exhibit merger or interaction signatures (21.5_(-3.3)^(+4.2)%) versus 7.8_(-1.3)^(+1.9)%). The increased merger fraction is significant at the 3.8σ level. If we exclude all point sources and consider only extended hosts, we find that the correlation between the merger fraction and obscuration is still evident, although at a reduced statistical significance (2.5σ). The fact that we observe a different disk/spheroid fraction versus obscuration indicates that the viewing angle cannot be the only thing differentiating our three AGN samples, as a simple unification model would suggest. The increased fraction of disturbed morphologies with obscuration supports an evolutionary scenario, in which Compton-thick AGNs are a distinct phase of obscured super-massive black hole (SMBH) growth following a merger/interaction event. Our findings also suggest that some of the merger-triggered SMBH growth predicted by recent AGN fueling models may be hidden among the heavily obscured, Compton-thick population.

Item Type:Article
Related URLs:
URLURL TypeDescription Paper
Brightman, Murray0000-0002-8147-2602
Nandra, Kirpal0000-0002-7150-9192
Koekemoer, Anton M.0000-0002-6610-2048
Salvato, Mara0000-0001-7116-9303
Aird, James0000-0003-1908-8463
Kartaltepe, Jeyhan S.0000-0001-9187-3605
Koo, David C.0000-0003-3385-6799
Lotz, Jennifer M.0000-0003-3130-5643
Additional Information:© 2015 American Astronomical Society. Received 2015 June 21; accepted 2015 September 9; published 2015 November 23. Support for Program number HST-GO-12060 was provided by NASA through a grant from the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Incorporated, under NASA contract NAS5-26555.
Funding AgencyGrant Number
Subject Keywords:galaxies: active; galaxies: evolution; X-rays: galaxies
Issue or Number:2
Record Number:CaltechAUTHORS:20151222-095220470
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Official Citation:Dale D. Kocevski et al 2015 ApJ 814 104
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:63127
Deposited By: Ruth Sustaita
Deposited On:22 Dec 2015 18:23
Last Modified:02 Dec 2019 18:29

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