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Title:
Inspiralling Supermassive Black Holes: A New Signpost for Galaxy Mergers
Authors:
Comerford, Julia M.; Gerke, Brian F.; Newman, Jeffrey A.; Davis, Marc; Yan, Renbin; Cooper, Michael C.; Faber, S. M.; Koo, David C.; Coil, Alison L.; Rosario, D. J.; Dutton, Aaron A.
Affiliation:
AA(Astronomy Department, 601 Campbell Hall, University of California, Berkeley, CA 94720, USA ), AB(Kavli Institute for Particle Astrophysics and Cosmology, M/S 29, Stanford Linear Accelerator Center, 2575 Sand Hill Rd., Menlo Park, CA 94725, USA ), AC(Department of Physics and Astronomy, University of Pittsburgh, Pittsburgh, PA 15260, USA ), AD(Department of Physics, University of California, Berkeley, CA 94720, USA ), AE(Department of Astronomy and Astrophysics, University of Toronto, Toronto, ON M5S 3H8, Canada ), AF(Steward Observatory, University of Arizona, Tucson, AZ 85721, USA ; Spitzer fellow. ), AG(UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA ), AH(UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA ), AI(Steward Observatory, University of Arizona, Tucson, AZ 85721, USA ; Department of Physics, University of California, San Diego, CA 92093, USA ; Hubble fellow.), AJ(UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA ), AK(UCO/Lick Observatory, Department of Astronomy and Astrophysics, University of California, Santa Cruz, CA 95064, USA )
Publication:
The Astrophysical Journal, Volume 698, Issue 1, pp. 956-965 (2009). (ApJ Homepage)
Publication Date:
06/2009
Origin:
IOP
ApJ Keywords:
galaxies: active, galaxies: interactions, galaxies: nuclei, galaxies: Seyfert
DOI:
10.1088/0004-637X/698/1/956
Bibliographic Code:
2009ApJ...698..956C

Abstract

We present a new technique for observationally identifying galaxy mergers spectroscopically rather than through host galaxy imaging. Our technique exploits the dynamics of supermassive black holes (SMBHs) powering active galactic nuclei (AGNs) in merger-remnant galaxies. Because structure in the universe is built up through galaxy mergers and nearly all galaxies host a central SMBH, some galaxies should possess two SMBHs near their centers as the result of a recent merger. These SMBHs spiral to the center of the resultant merger-remnant galaxy, and one or both of the SMBHs may power AGNs. Using the DEEP2 Galaxy Redshift Survey, we have examined 1881 red galaxies, of which 91 exhibit [O III] and Hβ emission lines indicative of Seyfert 2 activity. Of these, 32 AGNs have [O III] emission-line redshifts significantly different from the redshifts of the host galaxies' stars, corresponding to velocity offsets of ~50 km s-1 to ~300 km s-1. Two of these AGNs exhibit double-peaked [O III] emission lines, while the remaining 30 AGNs each exhibit a single set of velocity-offset [O III] emission lines. After exploring a variety of physical models for these velocity offsets, we argue that the most likely explanation is inspiralling SMBHs in merger-remnant galaxies. Based on this interpretation, we find that roughly half of the red galaxies hosting AGNs are also merger remnants, which implies that mergers may trigger AGN activity in red galaxies. The AGN velocity offsets we find imply a merger fraction of ~30% and a merger rate of ~3 mergers Gyr-1 for red galaxies at redshifts 0.34 < z < 0.82.
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