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We present a new set of index-based measurements of [$\alpha$/Fe] for asample of 2093 galaxies in the SAMI Galaxy Survey. Following earlier work, wefit a global relation between [$\alpha$/Fe] and the galaxy velocity dispersion$\sigma$ for red sequence galaxies,[$\alpha$/Fe]=(0.378$\pm$0.009)log($\sigma$/100)+(0.155$\pm$0.003). We observea correlation between the residuals and the local environmental surfacedensity, whereas no such relation exists for blue cloud galaxies. In the fullsample, we find that elliptical galaxies in high-density environments are$\alpha$-enhanced by up to 0.057$\pm$0.014 dex at velocity dispersions$\sigma$<100 km/s, compared with those in low-density environments. This$\alpha$-enhancement is morphology-dependent, with the offset decreasing alongthe Hubble sequence towards spirals, which have an offset of 0.019$\pm$0.014dex. At low velocity dispersion and controlling for morphology, we estimatethat star formation in high-density environments is truncated $\sim1$ Gyrearlier than in low-density environments. For elliptical galaxies only, we findsupport for a parabolic relationship between [$\alpha$/Fe] and $\sigma$, withan environmental $\alpha$-enhancement of at least 0.03 dex. This suggestsstrong contributions from both environment and mass-based quenching mechanisms.However, there is no evidence for this behaviour in later morphological types.

The SAMI Galaxy Survey: Trends in [\alpha/Fe] as a Function of Morphology and Environment