Abstract
Abstract Double-peaked narrow emission lines in active galactic nucleus (AGN) spectra can be produced by AGN outflows, rotation, or dual AGNs, which are AGN pairs in ongoing galaxy mergers. Consequently, double-peaked narrow AGN emission lines are useful tracers of the coevolution of galaxies and their supermassive black holes, as driven by AGN feedback and AGN fueling. We investigate this concept further with follow-up optical longslit observations of a sample of 95 Sloan Digital Sky Survey (SDSS) galaxies that have double-peaked narrow AGN emission lines. Based on a kinematic analysis of the longslit spectra, we confirm previous work that finds that the majority of double-peaked narrow AGN emission lines are associated with outflows. We also find that eight of the galaxies have companion galaxies with line-of-sight velocity separations <500 km s−1 and physical separations <30 kpc. Since we find evidence of AGNs in both galaxies, all eight of these systems are compelling dual AGN candidates. Galaxies with double-peaked narrow AGN emission lines occur in such galaxy mergers at least twice as often as typical active galaxies. Finally, we conclude that at least 3% of SDSS galaxies with double-peaked narrow AGN emission lines are found in galaxy mergers where both galaxies are resolved in SDSS imaging.
Highlights
Observational correlations between galaxies and their central supermassive black holes (e.g., Magorrian et al 1998; Gebhardt et al 2000; Marconi & Hunt 2003) indicate that supermassive black holes and galaxies are coupled as they evolve
In this paper we present and analyze follow-up observations for 95 galaxies in the Sloan Digital Sky Survey (SDSS) that have double-peaked narrow active galactic nucleus (AGN) emission lines in their spectra, which makes this the largest sample of such galaxies yet published in a follow-up observational paper
We classify a system as rotation dominated if it has Keplerian rotation in the plane of the galaxy, exhibited by Vr < 400 km s−1, σ1 < 500 km s−1, σ2 < 500 km s−1, and [O III] λ5007 emission that is aligned with the plane of the galaxy (e.g., Osterbrock & Ferland 2006)
Summary
Observational correlations between galaxies and their central supermassive black holes (e.g., Magorrian et al 1998; Gebhardt et al 2000; Marconi & Hunt 2003) indicate that supermassive black holes and galaxies are coupled as they evolve. Star formation driven and AGN driven outflows disperse the remaining gas in the merged galaxy systems, preventing the galaxies from becoming too massive (e.g., King 2003; Di Matteo et al 2005; Croton et al 2006; Fabian 2012) This feedback effect regulates both star formation and the growth of supermassive black holes, and helps merger remnants evolve to red, quiescent galaxies. Several hundred double-peaked narrow emission lines have been identified in spectroscopic surveys (Gerke et al 2007; Comerford et al 2009a; Wang et al 2009; Xu & Komossa 2009; Liu et al 2010b; Smith et al 2010; Ge et al 2012; Barrows et al 2013; Comerford et al 2013), with the largest samples found in the Sloan Digital Sky Survey (SDSS) These double-peaked line profiles can be produced by a variety of physical processes, including dual AGNs, AGN outflows, and disk rotation.
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