The SAMI galaxy survey: stellar population radial gradients in early-type galaxies

Ignacio Ferreras*, Nicholas Scott, Francesco La Barbera, Scott Croom, Jesse van de Sande, Andrew Hopkins, Matthew Colless, Tania M. Barone, Francesco d'Eugenio, Joss Bland-Hawthorn, Sarah Brough, Julia J. Bryant, Iraklis S. Konstantopoulos, Claudia Lagos, Jon S. Lawrence, Angel López-Sánchez, Anne M. Medling, Matt S. Owers, Samuel N. Richards

*Corresponding author for this work

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We study the internal radial gradients of the stellar populations in a sample comprising 522 early-type galaxies (ETGs) from the SAMI (Sydney-AAO Multi-object Integral field spectrograph) Galaxy Survey. We stack the spectra of individual spaxels in radial bins, and derive basic stellar population properties: total metallicity ([Z/H]), [Mg/Fe], [C/Fe] and age. The radial gradient (∇) and central value of the fits (evaluated at Re/4) are compared against a set of six observables that may act as drivers of the trends. We find that velocity dispersion (σ) - or, equivalently gravitational potential - is the dominant driver of the chemical composition gradients. Surface mass density is also correlated with the trends, especially with stellar age. The decrease of ∇[Mg/Fe] with increasing σ is contrasted by a rather shallow dependence of ∇[Z/H] with σ (although this radial gradient is overall rather steep). This result, along with a shallow age slope at the massive end, imposes a substantial constraint on the progenitors of the populations that contribute to the formation of the outer envelopes of ETGs. The SAMI sample is split, by design, between `field' and cluster galaxies. Only weak environment-related differences are found, most notably a stronger dependence of central total metallicity ([Z/H]e4) with σ along with a marginal trend of ∇[Z/H] to steepen in cluster galaxies, a result that is not followed by [Mg/Fe]. The results presented here serve as stringent constraints on numerical models of the formation and evolution of ETGs.

Original languageEnglish
Pages (from-to)608-622
Number of pages15
JournalMonthly Notices of the Royal Astronomical Society
Issue number1
Publication statusPublished - Oct 2019

Bibliographical note

This article has been accepted for publication in Monthly Notices of the Royal Astronomical Society, Volume 489, Issue 1, October 2019, Pages 608–622, Copyright 2019 The Author(s). Published by Oxford University Press on behalf of the Royal Astronomical Society. All rights reserved.


  • galaxies: elliptical and lenticular, cD
  • galaxies: evolution
  • galaxies: formation
  • galaxies: stellar content


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