The SAMI Galaxy Survey: the link between [α/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, λR e , drawn from the SAMI Galaxy Surv e y. We fit a global [ α/ Fe ]-σrelation, finding that [ α/ Fe ] = (0 . 395 ±0 . 010) log 10 ( σ) -(0 . 627 ±0 . 002). We observe an anti-correlation between the residuals Δ [ α/ Fe ] and the inclination-corrected λeo R e , which can be expressed as Δ [ α/ Fe ] = ( -0 . 057 ±0 . 008) λeo R e + (0 . 020 ±0 . 003). The anti-correlation appears to be driven by star-forming galaxies, with a gradient of Δ [ α/ Fe ] ∼( -0 . 121 ±0 . 015) λeo R e , although a weak relationship persists for the subsample of galaxies for which star formation has been quenched. We take this to be confirmation that disc-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 ∼0.5 Gyr to ∼1.2 Gyr from low- to high- λeo R e galaxies. Slow rotators do not appear to fit these trends. Their residual α-enhancement is indistinguishable from other galaxies with λeo R e ≲0 . 4, despite being both larger and more massive. This result shows that galaxies with λeo R e ≲ 0 . 4 experience a similar range of star formation histories, despite their different physical structure and angular momentum.