The ATLAS3D project - XXI. Correlations between gradients of local escape velocity and stellar populations in early-type galaxies

Nicholas Scott*, Michele Cappellari, Roger L. Davies, Gijs Verdoes Kleijn, Maxime Bois, Katherine Alatalo, Leo Blitz, Frédéric Bournaud, Martin Bureau, Alison Crocker, Timothy A. Davis, P. T. de Zeeuw, Pierre Alain Duc, Eric Emsellem, Sadegh Khochfar, Davor Krajnović, Harald Kuntschner, Richard M. McDermid, Raffaella Morganti, Thorsten Naab & 5 others Tom Oosterloo, Marc Sarzi, Paolo Serra, Anne Marie Weijmans, Lisa M. Young

*Corresponding author for this work

Research output: Contribution to journalArticle

56 Citations (Scopus)

Abstract

We explore the connection between the local escape velocity, Vesc, and the stellar population properties in the ATLAS3D survey, a complete, volume-limited sample of nearby early-type galaxies. We make use of ugriz photometry to construct Multi-Gaussian Expansion models of the surface brightnesses of our galaxies. We are able to fit the full range of surface brightness profiles found in our sample, and in addition we reproduce the results of state-ofthe- art photometry in the literature with residuals of 0.04 mag. We utilize these photometric models and SAURON integral-field spectroscopy, combined with Jeans dynamical modelling, to determine the local Vesc derived from the surface brightness. We find that the local Vesc is tightly correlated with the Mg b and Fe5015 line strengths and optical colours, and anticorrelated with the Hβ line strength. In the case of the Mg b and colour-Vesc relations we find that the relation within individual galaxies follows the global relation between different galaxies. We intentionally ignored any uncertain contribution due to dark matter since we are seeking an empirical description of stellar population gradients in early-type galaxies that is ideal for quantitative comparison with model predictions. We also make use of single stellar population (SSP) modelling to transform our line strength index measurements into the SSP-equivalent parameters age (t), metallicity ([Z/H]) and α-enhancement [α/Fe]. The residuals from the relation are correlated with age, [α/Fe], molecular gas mass and local environmental density. We identify a population of galaxies that occur only at low Vesc that exhibit negative gradients in the Mg b-and Colour-Vesc relations. These galaxies typically have young central stellar populations and contain significant amounts of molecular gas and dust. Combining these results with N-body simulations of binary mergers we use the Mgb-Vesc relation to constrain the possible number of dry mergers experienced by the local early-type galaxy population-a typical massive early-type galaxy can have experienced only ∼1.5 major mergers before becoming a significant outlier in the Mgb-Vesc relation.

Original languageEnglish
Pages (from-to)1894-1913
Number of pages20
JournalMonthly Notices of the Royal Astronomical Society
Volume432
Issue number3
DOIs
Publication statusPublished - Jun 2013
Externally publishedYes

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