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

We explore the connection between the local escape velocity, V esc, 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 o...

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Bibliographic Details
Published in:	Monthly notices of the Royal Astronomical Society 2013-07, Vol.432 (3), p.1894-1913
Main Authors:	Scott, Nicholas, Cappellari, Michele, Davies, Roger L, Kleijn, Gijs Verdoes, Bois, Maxime, Alatalo, Katherine, Blitz, Leo, Bournaud, Frédéric, Bureau, Martin, Crocker, Alison, Davis, Timothy A, de Zeeuw, P. T, Duc, Pierre-Alain, Emsellem, Eric, Khochfar, Sadegh, Krajnovi, Davor, Kuntschner, Harald, McDermid, Richard M, Morganti, Raffaella, Naab, Thorsten, Oosterloo, Tom, Sarzi, Marc, Serra, Paolo, Weijmans, Anne-Marie, Young, Lisa M
Format:	Article
Language:	eng
Subjects:	Astrophysics Physics
Online Access:	Get full text
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Summary:	We explore the connection between the local escape velocity, V esc, 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-of-the-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 V esc derived from the surface brightness. We find that the local V esc is tightly correlated with the Mg b and Fe5015 line strengths and optical colours, and anti-correlated with the Hβ line strength. In the case of the Mg b and colour-V esc 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 V esc that exhibit negative gradients in the Mg b- and Colour-V esc 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 Mg b-V esc 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 Mg b-V esc relation.
ISSN:	0035-8711 1365-2966