The SAMI Galaxy Survey: trends in [α/Fe] as a function of morphology and environment

Peter J. Watson*, Roger L. Davies, Sarah Brough, Scott M. Croom, Francesco D'Eugenio, Karl Glazebrook, Brent Groves, Ángel R. López-Sánchez, Jesse van de Sande, Nicholas Scott, Sam P. Vaughan, Jakob Walcher, Joss Bland-Hawthorn, Julia J. Bryant, Michael Goodwin, Jon S. Lawrence, Nuria P. F. Lorente, Matt S. Owers, Samuel Richards

*Corresponding author for this work

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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 ± 0.009)log10 (σ/100) + (0.155 ± 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 ± 0.014 dex at velocity dispersions σ < 100 km s-1, 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 ± 0.014 dex. At low velocity dispersion and controlling for morphology, we estimate that star formation in high-density environments is truncated ∼1 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.

Original languageEnglish
Pages (from-to)1541-1556
Number of pages16
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - 1 Feb 2022

Bibliographical note

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 510, Issue 1, February 2022, Pages 1541–1556, Copyright 2021 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


  • galaxies: evolution
  • galaxies: formation
  • galaxies: stellar content


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