Mergers trigger active galactic nuclei out to z ∼ 0.6

¹ Kapteyn Astronomical Institute, University of Groningen, Postbus 800, 9700 AV Groningen, The Netherlands
e-mail: gfymargaret@gmail.com
² SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
³ Department of Physics and Astronomy, University of Manitoba, Winnipeg, MB R3T 2N2, Canada
⁴ Department of Physics and Astronomy, 102 Natural Science Building, University of Louisville, Louisville, KY 40292, USA
⁵ Australian Astronomical Optics, Macquarie University, 105 Delhi Rd, North Ryde, NSW 2113, Australia
⁶ School of Physics and Astronomy, Monash University, Clayton, VIC 3800, Australia
⁷ Sydney Institute for Astronomy, School of Physics A28, University of Sydney, Sydney, NSW 2006, Australia
⁸ Department of Physics and Astronomy, Macquarie University, Sydney, NSW 2109, Australia
⁹ Astronomy, Astrophysics and Astrophotonics Research Centre, Macquarie University, Sydney, NSW 2109, Australia

Received: 22 November 2019
Accepted: 1 April 2020

Abstract

Aims. The fueling and feedback of active galactic nuclei (AGNs) are important for understanding the co-evolution between black holes and host galaxies. Mergers are thought to have the capability to bring gas inward and ignite nuclear activity, especially for more powerful AGNs. However, there is still significant ongoing debate on whether mergers can trigger AGNs and, if they do, whether mergers are a significant triggering mechanism.

Methods. We selected a low-redshift (0.005 <  z <  0.1) sample from the Sloan Digital Sky Survey and a high-redshift (0 <  z <  0.6) sample from the Galaxy And Mass Assembly survey. We took advantage of the convolutional neural network technique to identify mergers. We used mid-infrared (MIR) color cut and optical emission line diagnostics to classify AGNs. We also included low excitation radio galaxies (LERGs) to investigate the connection between mergers and low accretion rate AGNs.

Results. We find that AGNs are more likely to be found in mergers than non-mergers, with an AGN excess up to 1.81 ± 0.16, suggesting that mergers can trigger AGNs. We also find that the fraction of mergers in AGNs is higher than that in non-AGN controls, for both MIR and optically selected AGNs, as well as LERGs, with values between 16.40 ± 0.5% and 39.23 ± 2.10%, implying a non-negligible to potentially significant role of mergers in triggering AGNs. This merger fraction in AGNs increases as stellar mass increases, which supports the idea that mergers are more important for triggering AGNs in more massive galaxies. In terms of merger fraction as a function of AGN power we find a positive trend for MIR selected AGNs and a complex trend for optically selected AGNs, which we interpret under an evolutionary scenario proposed by previous studies. In addition, obscured MIR selected AGNs are more likely to be hosted in mergers than unobscured MIR selected AGNs.