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Durham University

Department of Physics

Staff profile

Publication details for Prof David Alexander

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. (2011). CANDELS constraining the AGN-merger connection with host morphologies at z ~ 2. The astrophysical journal 744(2): 148.

Author(s) from Durham


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.