Dynamical Mass Determinations and Scaling Relations of Early-Type Galaxies

TL;DR

This paper reviews how early-type galaxy scaling relations relate luminosity, size, and kinematics, emphasizing virial equilibrium, stellar population variations, and the role of dark matter within the half-light radius.

Contribution

It provides an updated understanding of dynamical scaling relations using unbiased mass profile determinations, highlighting the influence of stellar populations and bulge growth.

Findings

Scaling relations are driven by virial equilibrium.

Stellar mass-to-light ratio variations correlate with velocity dispersion.

Dark matter is negligible within the half-light radius.

Abstract

I review our understanding of classic dynamical scaling relations, relating luminosity, size and kinematics of early-type galaxies. Using unbiased determinations of galaxy mass profiles from stellar dynamical models, a simple picture has emerged in which scaling relations are driven by virial equilibrium, accompanied by a trend in the stellar mass-to-light ratio (M/L). This picture confirms the earliest insights. The trend is mainly due to the combined variation of age, metallicity and the stellar initial mass function (IMF). The systematic variations best correlate with the galaxy velocity dispersion, which traces the bulge mass fraction. This indicates a link between bulge growth and quenching of star formation. Dark matter is unimportant within the half-light radius, where the total mass profile is close to isothermal ($\rho\propto r^{-2}$).