Astronomy and Astrophysics – Astronomy
Scientific paper
May 2009
adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=2009dda....40.1505c&link_type=abstract
American Astronomical Society, DDA meeting #40, #15.05; Bulletin of the American Astronomical Society, Vol. 41, p.909
Astronomy and Astrophysics
Astronomy
Scientific paper
Although galaxy mergers play a fundamental role in the evolution of galaxies, they have proven difficult to identify observationally. We present here a new method for identifying galaxy mergers that exploits the dynamics of supermassive black holes (SMBHs) in galaxy mergers. Galaxies grow hierarchically through mergers and nearly every galaxy hosts a central SMBH, which implies that a merger between two galaxies can bring two SMBHs to the resultant merger-remnant galaxy. These SMBHs spiral to the center of the merger-remnant galaxy, and if sufficient gas is available for accretion one or both of the SMBHs may power an active galactic nucleus (AGN). We searched the DEEP2 Galaxy Redshift Survey for galaxies that host two SMBHs as the result of a recent merger, where both SMBHs are moving relative to the host galaxy and have not yet coalesced and settled at the bottom of the galaxy's potential well. If one or both SMBHs power AGN, such cases are identifiable by AGN-fueled [O III] emission lines that have a different redshift than the redshift of the galaxy's stellar absorption lines. A redshift difference corresponds to a velocity offset. Within the set of DEEP2 red galaxies at 0.3 < z < 0.8, we identified 32 AGN with statistically significant (greater than 3 sigma) velocity offsets, ranging from 50 km/s to 300 km/s. After exploring physical effects such as AGN outflows that could cause such offsets, we find that these offsets are most likely the result of SMBHs inspiralling within merger-remnant galaxies. With our new technique of identifying galaxy mergers, we find that roughly half of red galaxies hosting AGN are also merger remnants. This result implies that galaxy mergers may trigger AGN activity in red galaxies and sets a merger rate of 3 mergers/Gyr for red galaxies at 0.3 < z < 0.8.
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