The similar stellar populations of quiescent spiral and elliptical galaxies
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We compare the stellar population properties in the central regions of quiescent face-on spiral and elliptical log (M_*/M_sun) > 10.4 galaxies, for a visually classified galaxy sample in SDSS DR7 at 0.04<z<0.1. In particular, we analyze [Z/H], r-band light-weighted ages and \Delta(Mgb/), a tracer of the overabundance of \alpha-elements, for galaxies carefully selected to be composed by passive stellar populations. We construct samples of spiral and elliptical galaxies based on robust visual morphological classifications from Galaxy Zoo. At a given total stellar mass, quiescent spirals show slightly younger (~0.4 Gyrs), less \alpha-enhanced (\Delta(Mgb/) lower by 0.09) populations, while at a given central velocity dispersion they are more metal rich, but again at a very low level (0.03 dex).These trends can be attributed either to differences in dynamical structure or differences in stellar population properties. In any case, the small differences imply that, to first order, non-starforming spiral galaxies and ellipticals have very similar star-formation histories. Our passive spirals are carefully selected to not show any indications of ongoing star formation (obscured or unobscured) and thus are far from representative for all disk galaxies in the volume. Nonetheless, the main conclusion from our work is that those spiral galaxies which show no hints of ongoing star formation have stellar populations in their central regions equivalent to those of quiescent, bulge-dominated objects.
