The extent of ionization in simulations of radio-loud AGNs impacting kpc gas discs

Abstract

We use the results of relativistic hydrodynamic simulations of jet-ISM interactions in a galaxy with a radio-loud AGN to quantify the extent of ionization in the central few kpcs of the gaseous galactic disc. We perform post-process radiative transfer of AGN radiation through the simulated gaseous jet-perturbed disc to estimate the extent of photo-ionization by the AGN with an incident luminosity of $10^{45}\mathrm{erg}{\mathrm{s}}^{-1}$. We also map the gas that is collisionally ionized due to shocks driven by the jet. The analysis was carried out for simulations with similar jet power ($10^{45}\mathrm{erg}{\mathrm{s}}^{-1}$) but different jet orientations with respect to the gas disc. We find that the shocks from the jets can ionize a significant fraction (up to 33$\%$) of dense gas ($n>100\mathrm{c}{\mathrm{m}}^{-3}$) in the disc, and that the jets clear out the central regions of gas for AGN radiation to penetrate to larger distances in the disc. Jets inclined towards the disc plane couple more strongly with the ISM and ionize a larger fraction of gas in the disc as compared to the vertical jet. However, similar to previous studies, we find that the AGN radiation is quickly absorbed by the outer layers of dense clouds in the disc, and is not able to substantially ionize the disc on a global scale. Thus, compared to jet-ISM interactions, we expect that photo-ionization by the AGN radiation only weakly affects the star-formation activity in the central regions of the galactic disc ($\lesssim 1$ kpc), although the jet-induced shocks can spread farther out.

Published in MNRAS

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