Dale D. Kocevski, S. M. Faber, Mark Mozena, Anton M. Koekemoer, Kirpal Nandra, Cyprian Rangel, Elise S. Laird, Marcella Brusa, Stijn Wuyts, Jonathan R. Trump, David C. Koo, Rachel S. Somerville, Eric F. Bell, Jennifer M. Lotz, David M. Alexander, Frederic Bournaud, Christopher J. Conselice, Tomas Dahlen, Avishai Dekel, Jennifer L. DonleyJames S. Dunlop, Alexis Finoguenov, Antonis Georgakakis, Mauro Giavalisco, Yicheng Guo, Norman A. Grogin, Nimish P. Hathi, Stephanie Juneau, Jeyhan S. Kartaltepe, Ray A. Lucas, Elizabeth J. McGrath, Daniel H. McIntosh, Bahram Mobasher, Aday R. Robaina, David Rosario, Amber N. Straughn, Arjen van der Wel, Carolin Villforth

Research output: Contribution to journalArticlepeer-review


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 similar to 2. Our sample consists of 72 moderate-luminosity (L-X similar to 10(42-44) 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(-5.9)(+5.8)%), while a smaller percentage are found in spheroids (27.8(-4.6)(+5.8)%). Roughly 16.7(-3.5)(+5.3)% 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(-5.9)(+5.6)%) 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 similar to 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 similar to 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 similar to 2 than previously thought.

Original languageEnglish
Article number148
Pages (from-to)-
Number of pages9
JournalAstrophysical Journal
Issue number2
Publication statusPublished - 10 Jan 2012


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