Velocity dispersion functions of pressure-supported galaxies in EAGLE simulations with varying active galactic nucleus feedback

TL;DR

This study examines how different models of active galactic nucleus feedback in EAGLE simulations influence the stellar velocity dispersion functions of pressure-supported galaxies, revealing that VDF shape is sensitive to AGN feedback strength.

Contribution

It provides the first detailed analysis of the impact of various AGN feedback models on the stellar velocity dispersion functions in cosmological simulations.

Findings

VDFs are similar for standard and enhanced AGN feedback models.

Reduced or no AGN feedback leads to more high-dispersion galaxies.

Absence of AGN feedback results in increased central star formation.

Abstract

We investigate the stellar velocity dispersion functions (VDFs) of pressure-supported galaxies in the EAGLE cosmological simulations. The central stellar velocity dispersion is one of the fundamental dynamical tracers of the total mass of galaxy subhalos, alongside luminosity and stellar mass. Because it reflects the gravitational potential, the stellar velocity dispersion is expected to be relatively insensitive to feedback from Active Galactic Nuclei (AGN), a critical process that regulates the connection between other galaxy observables and subhalo mass. To examine the impact of AGN feedback, we analyze the VDFs from five EAGLE simulation runs, each adopting a different AGN feedback model: one "standard", two "enhanced", one "reduced", and one with no AGN feedback. We compute the stellar velocity dispersions of pressure-supported galaxies using member stellar particles, mimicking fiber spectroscopy. The VDFs from the standard and enhanced AGN feedback models show little difference. However, contrary to our initial expectation that the VDF shape would be largely insensitive to AGN feedback, the simulations with reduced and no AGN feedback show a significant excess of high velocity dispersion galaxies ($\sigma_{*}$ > 200 km s$^{-1}$) and a deficit of low dispersion galaxies (100 < $\sigma_{*}$ (km s$^{-1}$) < 200), compared to those with standard or enhanced AGN feedback. The presence of high velocity dispersion galaxies in the no-AGN model arises from enhanced central star formation, due to the absence of AGN-driven gas heating or expulsion. Our results demonstrate that the shape of the theoretical VDF is sensitive to the strength of AGN feedback. These predictions offer a theoretical benchmark for future observational studies of the galaxy velocity dispersion function using large-scale spectroscopic surveys.