Stellar Velocity Dispersion in Mergers: The Effects of Dust and Star Formation

TL;DR

This study examines how dust and star formation influence measurements of stellar velocity dispersion in merging disk galaxies, revealing that dust distribution significantly affects observational results and their comparison with simulations.

Contribution

It introduces a detailed analysis of dust and stellar evolution effects on velocity dispersion measurements using simulations and radiative transfer software.

Findings

Dust distribution impacts velocity dispersion measurements more than total attenuation.

Flux-weighted measurements are often higher than mass-weighted due to dust obscuration of young stars.

In some cases, flux-weighted measurements are lower when young stars are less obscured.

Abstract

We investigate the effects of stellar evolution and dust on measurements of stellar velocity dispersion in mergers of disk galaxies. $N$-body simulations and radiative transfer analysis software are used to obtain mass-weighted and flux-weighted measurements of stellar velocity dispersion. We find that the distribution of dust with respect to the distribution of young stars in such systems is more important than the total degree of attenuation. The presence of dust typically causes flux-weighted measurements of stellar velocity dispersion to be elevated with respect to mass-weighted measurements because dust preferentially obscures young stars, which tend to be dynamically cooler than older stellar populations in such systems. In exceptional situations, in which young stars are not preferentially obscured by dust, flux-weighted velocity dispersion measurements tend to be negatively offset with respect to mass-weighted measurements because the dynamically cool young stellar populations are more luminous, per unit mass, than older stellar populations. Our findings provide a context for comparing observationally-obtained measurements of velocity dispersion with measurements of velocity dispersion obtained from galaxy merger simulations.