CANDELS : constraining the AGN-merger connection with host morphologies at z ~ 2

Kocevski, D.D.; Faber, S.M.; Mozena, M.; Koekemoer, A.M.; Nandra, K.; Rangel, C.; Laird, E.S.; Brusa, M.; Wuyts, S.; Trump, J.R.; Koo, D.C.; Somerville, R.S.; Bell, E.F.; Lotz, J.M.; Alexander, D.M.; Bournaud, F.; Conselice, C.J.; Dahlen, T.; Dekel, A.; Donley, J.L.; Dunlop, J.S.; Finoguenov, A.; Georgakakis, A.; Giavalisco, M.; Guo, Y.; Grogin, N.A.; Hathi, N.P.; Juneau, S.; Kartaltepe, J.S.; Lucas, R.A.; McGrath, E.J.; McIntosh, D.H.; Mobasher, B.; Robaina, A.R.; Rosario, D.; Straughn, A.N.; Wel van der, A.; Villforth, C.

Abstract

Using Hubble Space Telescope/WFC3 imaging taken as part of the Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey, we examine the role that major galaxy mergers play in triggering active galactic nucleus (AGN) activity at z ~ 2. Our sample consists of 72 moderate-luminosity (L X ~ 1042-44 erg s-1) AGNs at 1.5 < z < 2.5 that are selected using the 4 Ms Chandra observations in the Chandra Deep Field South, the deepest X-ray observations to date. Employing visual classifications, we have analyzed the rest-frame optical morphologies of the AGN host galaxies and compared them to a mass-matched control sample of 216 non-active galaxies at the same redshift. We find that most of the AGNs reside in disk galaxies (51.4+5.8 - 5.9%), while a smaller percentage are found in spheroids (27.8+5.8 - 4.6%). Roughly 16.7+5.3 - 3.5% of the AGN hosts have highly disturbed morphologies and appear to be involved in a major merger or interaction, while most of the hosts (55.6+5.6 - 5.9%) appear relatively relaxed and undisturbed. These fractions are statistically consistent with the fraction of control galaxies that show similar morphological disturbances. These results suggest that the hosts of moderate-luminosity AGNs are no more likely to be involved in an ongoing merger or interaction relative to non-active galaxies of similar mass at z ~ 2. The high disk fraction observed among the AGN hosts also appears to be at odds with predictions that merger-driven accretion should be the dominant AGN fueling mode at z ~ 2, even at moderate X-ray luminosities. Although we cannot rule out that minor mergers are responsible for triggering these systems, the presence of a large population of relatively undisturbed disk-like hosts suggests that the stochastic accretion of gas plays a greater role in fueling AGN activity at z ~ 2 than previously thought.

Citation

Kocevski, D., Faber, S., Mozena, M., Koekemoer, A., Nandra, K., Rangel, C., …Villforth, C. (2011). CANDELS : constraining the AGN-merger connection with host morphologies at z ~ 2. Astrophysical Journal, 744(2), Article 148. https://doi.org/10.1088/0004-637x/744/2/148

• Journal Article Type: Article
• Publication Date: Jan 1, 2011
• Deposit Date: Jun 13, 2012
• Publicly Available Date: Jan 3, 2014
• Journal: Astrophysical Journal
• Print ISSN: 0004-637X
• Electronic ISSN: 1538-4357
• Publisher: American Astronomical Society
• Peer Reviewed: Peer Reviewed
• Volume: 744
• Issue: 2
• Article Number: 148
• DOI: https://doi.org/10.1088/0004-637x/744/2/148
• Keywords: Galaxies, Active, Evolution, X-rays.
• Public URL: https://durham-repository.worktribe.com/output/1476082