The Atlas3D Project - XXX. Star formation histories and stellar population scaling relations of early-type galaxies

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We present the stellar population content of early-type galaxies from the Atlas3D survey.

• Using spectra integrated within apertures covering up to one effective radius, we apply two methods: one based on measuring line-strength indices and applying single stellar population (SSP) models to derive SSP-equivalent values of stellar age, metallicity, and alpha enhancement; and one based on spectral fitting to derive non-parametric star-formation histories, mass-weighted average values of age, metallicity, and half-mass formation timescales.
• Using homogeneously derived effective radii and dynamically-determined galaxy masses, we present the distribution of stellar population parameters on the Mass Plane (M_JAM, Sigma_e, R_maj), showing that at fixed mass, compact early-type galaxies are on average older, more metal-rich, and more alpha-enhanced than their larger counterparts.
• From non-parametric star-formation histories, we find that the duration of star formation is systematically more extended in lower mass objects.