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 <SUB>X</SUB> ~ 10<SUP>42-44</SUP> erg s<SUP>-1</SUP>) 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<SUP>+5.8</SUP> <SUB>- 5.9</SUB>%), while a smaller percentage are found in spheroids (27.8<SUP>+5.8</SUP> <SUB>- 4.6</SUB>%). Roughly 16.7<SUP>+5.3</SUP> <SUB>- 3.5</SUB>% 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<SUP>+5.6</SUP> <SUB>- 5.9</SUB>%) 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.
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. Donley;J. 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. v. der;C. Villforth. - In: THE ASTROPHYSICAL JOURNAL. - ISSN 0004-637X. - STAMPA. - 744:(2012), pp. 148.148-148.156. [10.1088/0004-637X/744/2/148]
CANDELS: Constraining the AGN-Merger Connection with Host Morphologies at z ~ 2
BRUSA, MARCELLA;
2012
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.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
