Are Low Excitation Radio Galaxies Fuelled by Minor Mergers?
Date Submitted
2017-04-14 15:39:49
AGNsLocal
Yjan Gordon
E.A. Milne Centre for Astrophysics, University of Hull
Poster
Kevin Pimbblet (E.A. Milne Centre for Astrophysics), Matt Owers (Macquarie University), GAMA team (www.gama-survey.org)
Low Excitation Radio Galaxies (LERGs) are radio-loud active galactic nuclei with an absence of strong ionisation lines. LERGs are thought to be the result of weak, inefficient accretion onto the supermassive black hole (e.g. Narayan & Yi 1994; Hardcastle et al. 2007). Such inefficient accretion may be the result of a limited fuel supply to the central engine, either in the form of hot gas from an ageing stellar population or from a drip-feeding external process (Ellison, Patton & Hickox 2015). Should minor-mergers provide such an external source, then one might expect to see an excess of low mass satellites in the vicinity of LERGs relative to radio-quiet galaxies of similar mass and redshift.
We exploit the depth (r less than 19.8) and high spectroscopic completeness (greater than 98%) of the Galaxy And Mass Assembly (GAMA) survey to test this hypothesis for LERGs detected by the Faint Images of the Radio Sky at Twenty cm (FIRST) survey. GAMA is greater than 80% complete for stellar masses down to 10^9.25 solar masses out to a redshift of 0.12. At this redshift there are 18 LERGs in the GAMA footprint and we compare these to 1114 radio-quiet galaxies of similar stellar mass, redshift and group or field environment to the LERGs. We find no evidence of an excess of low mass satellites down to 10^9.25 solar masses, suggesting that if minor-mergers play a role in LERG fuelling, then the accreted satellites are less than 10^9.25 solar masses in stellar mass.