CANDELS: CONSTRAINING THE AGN–MERGER CONNECTION WITH HOST MORPHOLOGIES AT z ∼ 2

By D. Kocevski, S. Faber, M. Mozena, A. Koekemoer, K. Nandra, C. Rangel, E. Laird, M. Brusa, S. Wuyts, J. Trump and 28 more. 2011

281 citations recorded by the source corpus.

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 (LX ∼ 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.

Subfields: Astronomy and Astrophysics, Computer Vision and Pattern Recognition

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Citations in the corpus

The Coevolution of Galaxies and Supermassive Black Holes: Insights from Surveys of the Contemporary Universe (2014, background): “…over the same range in redshift (e.g. Pierce et al. 2007, Gabor et al. 2009, Hickox et al. 2009, Silverman et al. 2009, 2011, Schawinski et al. 2011, Kocevski et al. 2012, Mullaney et al. 2012a,b, Aird et al. 2012, 2013, Bohm et al. 2013, Rosario et al. 2013, Juneau et al. 2013, Chen et al. 2013).”
The mean star formation rate of X-ray selected active galaxies and its evolution from z~2.5: results from PEP-Herschel (2012, background): “Studies of moderate luminosity X-rayAGNs find no excess of merger signatures compared to inactive galaxies (e.g. Grogin et al. 2005), and only weak trends with AGN luminosity (Cisternas et al. 2011; Kocevski et al. 2012).”
Theoretical Challenges in Galaxy Formation (2016, background): “…at low and high redshift also provide evidence that significant black hole accretion is not solely connected to merging but also gas rich disk like galaxies can host AGN of significant luminosity (Cisternas et al. 2011, Georgakakis et al. 2009, Kocevski et al. 2012, Schawinski et al. 2011).”
The green valley is a red herring: Galaxy Zoo reveals two evolutionary pathways towards quenching of star formation in early-and late-type galaxies (2014, background): “The majority of black holes growing locally and at high redshift are hosted in late-type galaxies, clearly driven by secular processes rather than major mergers (e.g. Schawinski et al. 2010a, 2011, 2012; Cisternas et al. 2011; Kocevski et al. 2012; Simmons et al. 2012; Treister et al. 2012).”
SMOOTH(ER) STELLAR MASS MAPS IN CANDELS: CONSTRAINTS ON THE LONGEVITY OF CLUMPS IN HIGH-REDSHIFT STAR-FORMING GALAXIES (2012, methodology): “We mention in passing that object ID12328 serves as the prototype of 6 a merging system in the CANDELS visual classification effort (e.g., Kocevski et al. 2012; Kartaltepe et al. 2012).”
STRUCTURAL PARAMETERS OF GALAXIES IN CANDELS (2012, background): “Kocevski et al. (2012) compared the morphologies of galaxies that do and do not host AGN and concluded there is no significant difference, and Kartaltepe et al. (2011) found a tentative connection between extreme star formation activity and merging.”
CANDELS: THE PROGENITORS OF COMPACT QUIESCENT GALAXIES AT z ∼ 2 (2012, background): “This implies that, at these epochs, the majority of luminous (LX>10 43 erg/s) AGN are found preferentially in compact hosts, as opposed to lower redshifts, where AGN are more frequent in noncompact galaxies (Kocevski et al. 2012).”
BLACK HOLE VARIABILITY AND THE STAR FORMATION–ACTIVE GALACTIC NUCLEUS CONNECTION: DO ALL STAR-FORMING GALAXIES HOST AN ACTIVE GALACTIC NUCLEUS? (2013, background): “The weak dependence of the merger fraction on AGN luminosity at low LAGN may explain the observations that at moderate to high redshift, moderate-luminosity AGNs have indistinguishable merger fractions from normal galaxies (Cisternas et al. 2011; Schawinski et al. 2011; Kocevski et al. 2012).”
The Evolution of Galaxy Structure Over Cosmic Time (2014, background): “However, studies at higher redshifts generally do not find that more asymmetric or merging galaxies have a higher AGN fraction (e.g., Grogin et al. 2005; Gabor et al. 2009; Kocevski et al. 2012).”
MAJOR GALAXY MERGERS ONLY TRIGGER THE MOST LUMINOUS ACTIVE GALACTIC NUCLEI (2012, background): “This explains the conclusions of previous studies, mostly based on Xray surveys (e.g. Cisternas et al. 2011; Schawinski et al. 2011; Kocevski et al. 2012) of moderate luminosity AGN, which found that normal disk-dominated galaxies con- stitute the majority of the AGN host galaxies.”
Black holes on FIRE: stellar feedback limits early feeding of galactic nuclei (2017, result): “Our simulations thus predict that moderate luminosity active galactic nuclei (AGNs) at high redshift can be stochastically fueled and do not require major mergers events, in agreement with observations (e.g. Kocevski et al. 2012).”
Morphologies of z ∼ 0.7 AGN host galaxies in CANDELS: no trend of merger incidence with AGN luminosity (2014, methodology): “Kocevski et al. (2012) analysed human classifications of host galaxies of X-ray-selected AGN at z ≈ 2 with slightly higher luminosities than those studied in this paper.”
Cosmic X-ray surveys of distant active galaxies (2015, background): “However, as with the CMD analyses, clear differences mostly disappeared when the galaxy sample was matched in mass to the AGN sample (e.g., Kocevski et al 2012; Böhm et al 2013; Fan et al 2014; Villforth et al 2014); we note that recent evidence from a systematic morphological analysis of AGNs and…”
RELATIONS BETWEEN CENTRAL BLACK HOLE MASS AND TOTAL GALAXY STELLAR MASS IN THE LOCAL UNIVERSE (2015, result): “We find that a significant fraction of local broadline AGN host galaxies are also spirals/disks, similar to what has previously been found in studies of moderate-luminosity AGN host galaxies out to z ∼ 3 (e.g., Gabor et al. 2009; Schawinski et al. 2011; Kocevski et al. 2012; Bennert et al. 2015).”
THE HIDDEN “AGN MAIN SEQUENCE”: EVIDENCE FOR A UNIVERSAL BLACK HOLE ACCRETION TO STAR FORMATION RATE RATIO SINCE z ∼ 2 PRODUCING AN MBH–M* RELATION (2012, result): “This view is consistent with recent studies of the sSFRs and morphologies of X-ray selected AGN hosts which find that the AGN population is dominated by non-mergers (e.g., Cisternas et al. 2011b; Schawinski et al. 2011; Mullaney et al. 2012; Kocevski et al. 2012; Santini et al. 2012).”
Accreting supermassive black holes in the COSMOS field and the connection to their host galaxies (2012, background): “For example, major mergers are invoked to trigger bright quasars (e.g. Hopkins et al. 2008), while the role of major mergers in triggering more typical (∼L∗) AGNs is called into question (e.g. Cisternas et al. 2011; Schawinski et al. 2011; Kocevski et al. 2012).”