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.
Categories: astro-ph.GA