# The SAMI Galaxy Survey: mass-kinematics scaling relations

## TL;DR

This study uses SAMI Galaxy Survey data to establish a linear mass-kinematics relation combining rotation and dispersion, applicable across galaxy types with minimal scatter, improving understanding of galaxy dynamics.

## Contribution

It introduces a unified mass-kinematics scaling relation using $S_K$, applicable to all galaxy types, with less scatter than traditional relations, and compares stellar and gas kinematic measurements.

## Key findings

- The $ ext{log} M_* - ext{log} S_K$ relation is linear and consistent across galaxy types.
- The relation has smaller scatter than Tully-Fisher and Faber-Jackson relations.
- The relation's scatter is minimally affected by the choice of $K$ parameter.

## Abstract

We use data from the Sydney-AAO Multi-object Integral-field spectroscopy (SAMI) Galaxy Survey to study the dynamical scaling relation between galaxy stellar mass $M_*$ and the general kinematic parameter $S_K = \sqrt{K V_{rot}^2 + \sigma^2}$ that combines rotation velocity $V_{rot}$ and velocity dispersion $\sigma$. We show that the $\log M_* - \log S_K$ relation: (1)~is linear above limits set by properties of the samples and observations; (2)~has slightly different slope when derived from stellar or gas kinematic measurements; (3)~applies to both early-type and late-type galaxies and has smaller scatter than either the Tully-Fisher relation ($\log M_* - \log V_{rot}$) for late types or the Faber-Jackson relation ($\log M_* - \log\sigma$) for early types; and (4)~has scatter that is only weakly sensitive to the value of $K$, with minimum scatter for $K$ in the range 0.4 and 0.7. We compare $S_K$ to the aperture second moment (the `aperture velocity dispersion') measured from the integrated spectrum within a 3-arcsecond radius aperture ($\sigma_{3^{\prime\prime}}$). We find that while $S_{K}$ and $\sigma_{3^{\prime\prime}}$ are in general tightly correlated, the $\log M_* - \log S_K$ relation has less scatter than the $\log M_* - \log \sigma_{3^{\prime\prime}}$ relation.