Ionized Outflows in Low Excitation Radio Galaxies — Radiation Driven

Low excitation radio galaxies (LERGs) are weakly accreting active galactic nuclei (AGN) believed to be fuelled by radiatively inefficient accretion processes. Recently, studies have found evidence for gas outflows in these galaxies, suspected to be driven by the AGN jets. To investigate the mechanisms responsible for such outflows, we select 801 LERGs using the Best & Heckman (2012) catalogue of radio galaxies at z < 0.3. Exploiting the availability of Sloan Digital Sky Survey spectra for this sample, we detect ionized outflows in 1.5 % of LERGs based on modelling the [O III] (5007A) emission line complex. The black hole accretion rates in LERGs with outflows are found to be close to 1 % of the Eddington limit, and thus represent the high end of the LERG accretion rate distribution. Furthermore by using 1.4 GHz imaging from the Faint Images of the Radio Sky at Twenty Centimeters survey we find the distribution of radio morphologies in LERGs with outflows to be representative of the parent LERG population. Our results are therefore consistent with ionized gas outflows in LERGs being the result of radiation pressure from the accretion flow, rather than being jet driven.