Effects of Baryon Dissipation on the Dark Matter Virial Scaling Relation

TL;DR

This study uses cosmological simulations to show that baryon dissipation slightly increases dark matter velocity dispersion and affects galaxy velocity bias, with implications for interpreting cluster observations and cosmological data.

Contribution

It demonstrates how baryon dissipation influences dark matter virial relations and galaxy velocity bias, providing guidance for observational analysis of clusters.

Findings

Baryon dissipation increases dark matter velocity dispersion by 5-10%.

Galaxy velocity bias depends on selection criteria, with stellar mass-selected galaxies showing no bias.

Using more than twenty massive galaxies yields unbiased velocity dispersion estimates.

Abstract

We investigate effects of baryon dissipation on the dark matter virial scaling relation between total mass and velocity dispersion and the velocity bias of galaxies in groups and clusters using self-consistent cosmological simulations. We show that the baryon dissipation increases the velocity dispersion of dark matter within the virial radius by 5% - 10%. The effect is mainly driven by the change in density and gravitational potential in inner regions of cluster, and it is larger in lower mass systems where gas cooling and star formation are more efficient. We also show that the galaxy velocity bias depends on how galaxies are selected. Galaxies selected based on their stellar mass exhibit no velocity bias, while galaxies selected based on their total mass show positive bias of ~10%, consistent with previous results based on collisionless dark matter- only simulations. We further find that observational estimates of galaxy velocity dispersion are unbiased with respect to the velocity dispersion of dark matter, provided galaxies are selected using their stellar masses and and their velocity dispersions are computed with more than twenty most massive galaxies. Velocity dispersions estimated with fewer galaxies, on the other hand, can lead to significant underestimate of dynamical masses. Results presented in this paper should be useful in interpretating high-redshift groups and clusters as well as cosmological constraints derived from upcoming optical cluster surveys.