CANDELS: Constraining the AGN-Merger Connection with Host Morphologies at z 2

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

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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.
Original languageEnglish
Pages (from-to)148
Number of pages1
JournalAstrophysical Journal
Volume744
Issue number2
DOIs
Publication statusPublished - 2012

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Kocevski, D. D., Faber, S. M., Mozena, M., Koekemoer, A. M., Nandra, K., Rangel, C., ... Villforth, C. (2012). CANDELS: Constraining the AGN-Merger Connection with Host Morphologies at z 2. Astrophysical Journal, 744(2), 148. https://doi.org/10.1088/0004-637X/744/2/148