Galaxy pairs in the Sloan Digital Sky Survey - IV: Interactions trigger AGN

By Sara L. Ellison, David R. Patton, J. Trevor Mendel, J. Scudder. 2011

250 citations recorded by the source corpus.

Galaxy-galaxy interactions are predicted to cause gas inflows leading to enhanced nuclear star formation. In this paper we test the further prediction that the gas inflows lead to enhanced accretion onto the central supermassive black hole, triggering activity in the nucleus. Based on a sample of 11,060 SDSS galaxies with a close companion (rp < 80 kpc, Delta V < 200 km/s), we classify AGN based either on emission line ratios or on spectral classification as a quasar. The AGN fraction in the close pairs sample is compared to a control sample of 110,600 mass- and redshift-matched control galaxies with no nearby companion. We find a clear increase in the AGN fraction in close pairs of galaxies with projected separations < 40 kpc by up to a factor of 2.5 relative to the control sample (although the enhancement depends on the chosen S/N cut of the sample). The increase in AGN fraction is strongest in equal mass galaxy pairings, and weakest in the lower mass component of an unequal mass pairing. The increased AGN fraction at small separations is accompanied by an enhancement in the number of `composite' galaxies whose spectra are the result of photoionization by both AGN and stars. Our results indicate that AGN activity occurs (at least in some cases) well before final coalescence and concurrently with ongoing star formation. Finally, we find a marked increase at small projected separations of the fraction of pairs in which BOTH galaxies harbour AGN. We demonstrate that the fraction of double AGN exceeds the expected random fraction, indicating that some pairs undergo correlated nuclear activity. Taken together with complimentary studies, we favour an interpretation where interactions trigger AGN, but are not the only cause of nuclear activity.

Subfields: Astronomy and Astrophysics, Instrumentation

View Paper: https://www.semanticscholar.org/paper/e400d1cc5c6ad0d0fec2c494af9b16829625c44e

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Citations in the corpus

Galaxy pairs in the Sloan Digital Sky Survey – V. Tracing changes in star formation rate and metallicity out to separations of 80 kpc (2012, background): “Ellison et al. (2011) found that in galaxy pairs at small separations, a galaxy hosting an AGN was twice as likely to have a companion also hosting an AGN than would be expected at random.”
The quest for dual and binary supermassive black holes: A multi-messenger view (2019, background): “…mentioning that in the study of a large sample of galaxy pairs selected in the mid-IR, the fraction of AGN, relative to a mass-, redshift- and environment-matched control sample, increases with decreasing projected sepa- ration (Ellison et al., 2011; Satyapal et al., 2014, see discussion in Sect.”
Growing supermassive black holes in the late stages of galaxy mergers are heavily obscured (2017, background): “…luminosity (see also Bessiere et al. 2012; Schawinski et al. 2012; Hickox et al. 2014; Glikman et al. 2015), and observations of optically-selected (Ellison et al. 2011), IR-selected (Satyapal et al. 2014) and X-ray selected (Silverman et al. 2011; Koss et al. 2012) samples of pairs have shown…”
Galaxy pairs in the Sloan Digital Sky Survey – IX. Merger-induced AGN activity as traced by the Wide-field Infrared Survey Explorer (2014, methodology): “…work on galaxy pairs and post-mergers in the Sloan Digital Sky Survey, we have used optical emission line diagnostics to identify an enhanced AGN fraction relative to a control that increases with decreasing pair separations (Ellison et al. 2011) and peaks post-coalescence (Ellison et al. 2013).”
Galaxy Interactions Trigger Rapid Black Hole Growth: an unprecedented view from the Hyper Suprime-Cam Survey (2017, background): “By contrast, others find evidence supporting a correlation between merging and AGN in some more nearby galaxies (e.g., Koss et al. 2010; Ellison et al. 2011b; Silverman et al. 2011; Ellison et al. 2013; Satyapal et al. 2014a; Hong et al. 2015; Weston et al. 2017).”
Bulge mass is king: the dominant role of the bulge in determining the fraction of passive galaxies in the Sloan Digital Sky Survey (2014, background): “Galaxy mergers and interactions are also found to enhance nuclear activity (e.g. Ellison et al. 2011, Silverman et al. 2011, Ellison et al. 2013) and thus couple to increased AGN feedback as well.”
Galaxy and mass assembly (GAMA): End of survey report and data release 2 (2015, background): “…triggering (e.g. Hopkins et al. 2013a; Patton et al. 2013) and truncating (e.g. Hopkins et al. 2008) star formation, fuelling central supermassive black holes (e.g. Di Matteo, Springel & Hernquist 2005; Ellison et al. 2011), and structural and size evolution (e.g. Naab, Johansson & Ostriker 2009).”
Galaxy pairs in the Sloan Digital Sky Survey – VIII. The observational properties of post-merger galaxies (2013, background): “However, whereas in Ellison et al. (2011) we found an AGN excess only out to rp ∼ 40 h−170 kpc, in the present analysis we find a statistical excess out to at least 80 h−170 kpc, where AGN are more common by 10–20 per cent than in the control sample.”
Morphologies of z ∼ 0.7 AGN host galaxies in CANDELS: no trend of merger incidence with AGN luminosity (2014, result): “The higher incidence of close-by companions is also consistent with merger triggering at an early stage of mergers, as found in many other studies (Koss et al. 2010; Ellison et al. 2011; Silverman et al. 2011; Liu, Shen & Strauss 2012; Villforth, Sarajedini & Koekemoer 2012).”
Growth and activity of black holes in galaxy mergers with varying mass ratios (2014, methodology): “Ellison et al. (2011), Silverman et al. (2011) and Ellison et al. (2013) study the enhancement in the AGN fraction for galaxies in pairs with respect to isolated galaxies.”
The cosmic evolution of massive black holes in the Horizon-AGN simulation (2016, background): “Observations also find an enhancement of AGN activity in galaxies with companions (Ellison et al. 2008, 2011; Silverman et al. 2011; Koss et al. 2012; Lackner et al. 2014).”
Galaxy pairs in the Sloan Digital Sky Survey – VI. The orbital extent of enhanced star formation in interacting galaxies (2013, background): “These enhancements are accompanied by bluer central colours (Patton et al. 2011), diluted metallicities (Scudder et al. 2012), and an increased incidence of active galactic nuclei(AGNs; Ellison et al. 2011) and luminous infrared galaxies (Ellison et al. 2013).”