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

• Main Authors: Watson, Peter J., Davies, Roger L., Brough, Sarah, Croom, Scott M., D'Eugenio, Francesco, Glazebrook, Karl, Groves, Brent, López-Sánchez, Ángel R., van de Sande, Jesse, Scott, Nicholas, Vaughan, Sam P., Walcher, Jakob, Bland-Hawthorn, Joss, Bryant, Julia J., Goodwin, Michael, Lawrence, Jon S., Lorente, Nuria P. F., Owers, Matt S., Richards, Samuel
• Format: Article in Journal/Newspaper
• Language: unknown
• Published: arXiv 2021
• Subjects: Astrophysics of Galaxies astro-ph.GA; FOS Physical sciences; Hubble; sami
• Online Access: https://dx.doi.org/10.48550/arxiv.2106.01928; https://arxiv.org/abs/2106.01928

We present a new set of index-based measurements of [$α$/Fe] for a sample of 2093 galaxies in the SAMI Galaxy Survey. Following earlier work, we fit a global relation between [$α$/Fe] and the galaxy velocity dispersion $σ$ for red sequence galaxies, [$α$/Fe]=(0.378$\pm$0.009)log($σ$/100)+(0.155$\pm$0.003). We observe a correlation between the residuals and the local environmental surface density, whereas no such relation exists for blue cloud galaxies. In the full sample, we find that elliptical galaxies in high-density environments are $α$-enhanced by up to 0.057$\pm$0.014 dex at velocity dispersions $σ$<100 km/s, compared with those in low-density environments. This $α$-enhancement is morphology-dependent, with the offset decreasing along the Hubble sequence towards spirals, which have an offset of 0.019$\pm$0.014 dex. At low velocity dispersion and controlling for morphology, we estimate that star formation in high-density environments is truncated $\sim1$ Gyr earlier than in low-density environments. For elliptical galaxies only, we find support for a parabolic relationship between [$α$/Fe] and $σ$, with an environmental $α$-enhancement of at least 0.03 dex. This suggests strong contributions from both environment and mass-based quenching mechanisms. However, there is no evidence for this behaviour in later morphological types. : 15 pages, 9 figures. Revised after comments from referee