Contributed Talk - Splinter SMBHs

Wednesday, 23 September 2020, 11:40   (virtual room K)

AGN-driven outflows and the AGN feedback efficiency in young radio galaxies

F. Santoro, C. Tadhunter, D.Baron, R.Morganti
MPIA Heidelberg, University of Sheffield, Tel-Aviv University, ASTRON, Kapteyn Institute Groningen

AGN feedback operated by the expansion of radio jets can play a crucial role in driving gaseous outflows on galaxy scales. Galaxies hosting young radio AGN, whose jets are in the first phases of expansion through the surrounding ISM, are the ideal targets to probe the energetic significance of this mechanism. In this talk I will characterise the warm ionised gas outflows in a sample of 9 young radio sources from the 2Jy sample. Combining X-shooter spectroscopy and HST imaging data, we found that the warm outflows have similar radial extents ( about 0.06 - 2 kpc) to radio sources, confirming that `jet mode' AGN feedback is likely the dominant driver of the outflows detected in young radio galaxies. I will show how, exploiting the broad spectral coverage of the X-shooter data, we have used the ratios of trans-auroral emission lines of [SII] and [OII] to estimate the gas electron densities, finding that most of the outflows contain dense gas (log(n_e)~3 - 4.8), possibly indicative of some level of compression associated with the jet-induced feedback. We find that the kinetic powers of the warm outflows are a relatively small fraction of the energies available from the accretion of material onto the central SMBH, reflecting AGN feedback efficiencies below 1% in most cases. To put our study in a broader context, I will then compare our results with an heterogeneous collection of AGN-driven outflows from the literature, emphasising the sensitivity of the derived outflow properties (e.g. masses, energetics, feedback efficiency) to the precision with which the electron densities are measured. Overall, the warm outflows detected in our sample are strikingly similar to those found in nearby ULIRGs, but more energetic and with a high feedback efficiencies on average than the general population of nearby AGN of similar bolometric luminosity. We argue that this is likely to reflect the high degree of coupling between the jets and the near-nuclear ISM in the early stages of radio source evolution.