The SAMI Galaxy Survey: The contribution of different kinematic classes to the stellar mass function of nearby galaxies

TL;DR

This study uses the SAMI Galaxy Survey to analyze how different kinematic classes of galaxies contribute to the stellar mass function, revealing that fast rotators dominate the mass budget and many galaxies have significant cold disk components.

Contribution

It provides a detailed kinematic classification of galaxies and quantifies the stellar mass contribution of various dynamical types, including cold disks, in the local Universe.

Findings

Fast rotators account for over 80% of stellar mass.

Dynamically cold disks contribute at least 25% of stellar mass.

Many visually two-component galaxies have kinematics consistent with cold disks.

Abstract

We use the complete Sydney-AAO Multi-object Integral field spectrograph (SAMI) Galaxy Survey to determine the contribution of slow rotators, as well as different types of fast rotators, to the stellar mass function of galaxies in the local Universe. We use stellar kinematics not only to discriminate between fast and slow rotators, but also to distinguish between dynamically cold systems (i.e., consistent with intrinsic axis ratios$<0.3$) and systems including a prominent dispersion-supported bulge. We show that fast rotators account for more than $80\%$ of the stellar mass budget of nearby galaxies, confirming that their number density overwhelms that of slow rotators at almost all masses from $10^{9}$ to $10^{11.5}{\rm M_\odot}$. Most importantly, dynamically cold disks contribute to at least $25\%$ of the stellar mass budget of the local Universe, significantly higher than what is estimated from visual morphology alone. For stellar masses up to $10^{10.5}{\rm M_\odot}$, this class makes up $>=30\%$ of the galaxy population in each stellar mass bin. The fact that many galaxies that are visually classified as having two-components have stellar spin consistent with dynamically cold disks suggests that the inner component is either rotationally-dominated (e.g., bar, pseudo-bulge) or has little effect on the global stellar kinematics of galaxies.