The SAMI Galaxy Survey: the link between [α/Fe] and kinematic morphology

We explore a sample of 1492 galaxies with measurements of the mean stellar population properties and the spin parameter proxy, λ_Re⁠, drawn from the SAMI Galaxy Survey. We fit a global [α/Fe]–σ relation, finding that [α/Fe]=(0.395±0.010)log₁₀(σ)−(0.627±0.002)⁠. We observe an anti-correlation between the residuals Δ[α/Fe] and the inclination-corrected λ^eo_Re⁠, which can be expressed as Δ[α/Fe]=(−0.057±0.008)λ^eo_Re+(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)λ^eo_Re⁠, 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-λ^eo_Re galaxies. Slow rotators do not appear to fit these trends. Their residual α-enhancement is indistinguishable from other galaxies with λ^eo_Re⪅0.4⁠, despite being both larger and more massive. This result shows that galaxies with λ^eo_Re⪅0.4 experience a similar range of star formation histories, despite their different physical structure and angular momentum.