Capturing the inside-out quenching by black holes with far-infrared atomic line ratios

Abstract

We propose to use relative strengths of far-infrared fine structure lines from galaxies to characterise early phases of the inside-out quenching by massive black holes (BHs). The BH feedback is thought to quench star formation by evacuating the ambient gas. In order to quantify the feedback effect on the gas density in the galactic centres, we utilise the outputs of IllustrisTNG and Illustris simulations, which implement different BH feedback models. We devise a physical model of H II regions and compute the intensities of [O III ] 52 and 88 µm lines. The line intensity ratio is sensitive to the local electron density, and thus can be used to measure the strength and physical extent of the BH quenching. If the BH feedback abruptly operates and expel the gas when it grows to a certain mass, as modelled in IllustrisTNG, the low-density gas yields relatively weak [O III ] 52 line with respect to 88 µm. In contrast, if the feedback strength and hence the local gas density are not strongly correlated with the BH mass, as in Illustris, the line ratio is not expected to vary significantly among galaxies with different evolutionary stages. We find these features are reproduced in the simulations. We also show that the line ratios are not sensitive to the aperture size for measurement, and thus observations do not need to resolve the galactic centres. We argue that the integrated line ratios can be used to capture the onset of the inside-out quenching by BHs.

High-resolution synthetic UV-submm images for simulated Milky Way-type galaxies from the Auriga project

“…It would be useful, for example, to compare with the concentration indices of Illustris-TNG (Pillepich et al 2019) disky galaxies of comparable mass and SFR. The Illustris-TNG AGN feedback model (Pillepich et al 2018;Weinberger et al 2018) employs a kinetic feedback at low black hole accretion rates, which leads to a different central gas structure and composition (Terrazas et al 2020;Inoue et al 2021). The Illustris-TNG stellar wind feedback model (Pillepich et al 2018) is also significantly different in comparison to that used in Auriga.…”