The SAMI Galaxy Survey: Towards a unified dynamical scaling relation for
  galaxies of all types
  We take advantage of the first data from the Sydney-AAO Multi-object Integral
field (SAMI) Galaxy Survey to investigate the relation between the kinematics
of gas and stars, and stellar mass in a comprehensive sample of nearby
galaxies. We find that all 235 objects in our sample, regardless of their
morphology, lie on a tight relation linking stellar mass ($M_{*}$) to internal
velocity quantified by the $S_{0.5}$ parameter, which combines the contribution
of both dispersion ($\sigma$) and rotational velocity ($V_{rot}$) to the
dynamical support of a galaxy ($S_{0.5}=\sqrt{0.5V_{rot}^{2}+\sigma^{2}}$). Our
results are independent of the baryonic component from which $\sigma$ and
$V_{rot}$ are estimated, as the $S_{0.5}$ of stars and gas agree remarkably
well. This represents a significant improvement compared to the canonical
$M_{*}$ vs. $V_{rot}$ and $M_{*}$ vs. $\sigma$ relations. Not only is no sample
pruning necessary, but also stellar and gas kinematics can be used
simultaneously, as the effect of asymmetric drift is taken into account once
$V_{rot}$ and $\sigma$ are combined. Our findings illustrate how the
combination of dispersion and rotational velocities for both gas and stars can
provide us with a single dynamical scaling relation valid for galaxies of all
morphologies across at least the stellar mass range
8.5$<log(M_{*}/M_{\odot})<$11. Such relation appears to be more general and at
least as tight as any other dynamical scaling relation, representing a unique
tool for investigating the link between galaxy kinematics and baryonic content,
and a less biased comparison with theoretical models.
