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

• Published in: Monthly Notices of the Royal Astronomical Society
• Main Authors: Ferreras, Ignacio, Scott, Nicholas, La Barbera, Francesco, Croom, Scott, van de Sande, Jesse, Hopkins, Andrew, Colless, Matthew, Barone, Tania M., d'Eugenio, Francesco, Bland-Hawthorn, Joss, Brough, Sarah, Bryant, Julia J., Konstantopoulos, Iraklis S., Lagos, Claudia, Lawrence, Jon S., López-Sánchez, Angel, Medling, Anne M., Owers, Matt S., Richards, Samuel N.
• Format: Article in Journal/Newspaper
• Language: English
• Published: 2019
• Subjects: galaxies: elliptical and lenticular; cD; galaxies: evolution; galaxies: formation; galaxies: stellar content; sami
• Online Access: https://researchers.mq.edu.au/en/publications/c1b9025f-f3b2-4c2f-873a-499400a2e290; https://doi.org/10.1093/mnras/stz2095; https://research-management.mq.edu.au/ws/files/117798944/117699477.pdf; http://purl.org/au-research/grants/arc/FT140100255; http://www.scopus.com/inward/record.url?scp=85075234754&partnerID=8YFLogxK

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 R e /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.