The SAMI Galaxy Survey: The Link Between [$\hat{I}\pm$/Fe] and Kinematic Morphology

Abstract

We explore a sample of 1492 galaxies with measurements of the mean stellar population properties and the spin parameter proxy, $\hat{I}{»}_{R_{\mathrm{e}}}$, drawn from the SAMI Galaxy Survey. We fit a global $\left[\hat{I}\pm /\mathrm{Fe}\right]$-$\ddot{I}ƒ$ relation, finding that $\left[\hat{I}\pm /\mathrm{Fe}\right]=(0.395\pm 0.010){\log }_{10}\left(\ddot{\mathrm{I}}ƒ\right)-(0.627\pm 0.002)$. We observe an anti-correlation between the residuals $\hat{I}”\left[\hat{I}\pm /\mathrm{Fe}\right]$ and the inclination-corrected $\hat{I}{»}_{R_{\mathrm{e}}}^{\mathrm{eo}}$, which can be expressed as $\hat{I}”\left[\hat{I}\pm /\mathrm{Fe}\right]=(-0.057\pm 0.008)\hat{I}{»}_{R_{\mathrm{e}}}^{\mathrm{eo}}+(0.020\pm 0.003)$. The anti-correlation appears to be driven by star-forming galaxies, with a gradient of $\hat{I}”\left[\hat{I}\pm /\mathrm{Fe}\right]\sim (-0.121\pm 0.015)\hat{I}{»}_{R_{\mathrm{e}}}^{\mathrm{eo}}$, although a weak relationship persists for the subsample of galaxies for which star formation has been quenched. We take this to be confirmation that disk-dominated galaxies have an extended duration of star formation. At a reference velocity dispersion of 200 km s${}^{-1}$, we estimate an increase in half-mass formation time from $\sim$0.5 Gyr to $\sim$1.2 Gyr from low- to high-$\hat{I}{»}_{R_{\mathrm{e}}}^{\mathrm{eo}}$ galaxies. Slow rotators do not appear to fit these trends. Their residual $\hat{I}\pm$-enhancement is indistinguishable from other galaxies with $\hat{I}{»}_{R_{\mathrm{e}}}^{\mathrm{eo}}⪅0.4$, despite being both larger and more massive. This result shows that galaxies with $\hat{I}{»}_{R_{\mathrm{e}}}^{\mathrm{eo}}⪅0.4$ experience a similar range of star formation histories, despite their different physical structure and angular momentum.

12 pages, 9 figures