The failure of stellar feedback, magnetic fields, conduction, and morphological quenching in maintaining red galaxies

TL;DR

This study uses high-resolution simulations to show that stellar feedback, magnetic fields, conduction, and morphological quenching alone cannot prevent cooling flows or maintain galaxy quenching in halos from 10^{12} to 10^{14} solar masses, implying the necessity of AGN feedback.

Contribution

The paper demonstrates through simulations that non-AGN physics are insufficient to sustain galaxy quenching, highlighting the need for additional mechanisms like AGN feedback.

Findings

Stellar feedback alters cold/warm gas balance but not baryonic inflow.

Conduction reduces inflow only in the most massive halos, by about a factor of 2.

Morphological changes have negligible impact on cooling flows.

Abstract

The quenching "maintenance'" and related "cooling flow" problems are important in galaxies from Milky Way mass through clusters. We investigate this in halos with masses $\sim 10^{12}-10^{14}\,{\rm M}_{\odot}$, using non-cosmological high-resolution hydrodynamic simulations with the FIRE-2 (Feedback In Realistic Environments) stellar feedback model. We specifically focus on physics present without AGN, and show that various proposed "non-AGN" solution mechanisms in the literature, including Type Ia supernovae, shocked AGB winds, other forms of stellar feedback (e.g. cosmic rays), magnetic fields, Spitzer-Braginskii conduction, or "morphological quenching" do not halt or substantially reduce cooling flows nor maintain "quenched" galaxies in this mass range. We show that stellar feedback (including cosmic rays from SNe) alters the balance of cold/warm gas and the rate at which the cooled gas within the galaxy turns into stars, but not the net baryonic inflow. If anything, outflowing metals and dense gas promote additional cooling. Conduction is important only in the most massive halos, as expected, but even at $\sim 10^{14}\,{\rm M}_{\odot}$ reduces inflow only by a factor $\sim 2$ (owing to saturation effects and anisotropic suppression). Changing the morphology of the galaxies only slightly alters their Toomre-$Q$ parameter, and has no effect on cooling (as expected), so has essentially no effect on cooling flows or maintaining quenching. This all supports the idea that additional physics, e.g., AGN feedback, must be important in massive galaxies.