The distribution of local star formation activity as a function of galaxy stellar mass, environment and morphology

Abstract

We present a detailed inventory of star formation in the local Universe, dissecting the cosmic star formation budget as a function of key variables that influence the star formation rate (SFR) of galaxies: stellar mass, local environment and morphology. We use a large homogeneous data set from the Sloan Digital Sky Survey to first study how the star formation budget in galaxies with stellar masses greater than log(M*/M⊙) = 10 splits as a function of each parameter separately. We then explore how the budget behaves as a simultaneous function of these three parameters. We show that the bulk of the star formation at z < 0.075 (∼65 per cent) takes place in spiral galaxies that reside in the field, and have stellar masses between 10 < log(M*/M⊙) < 10.9. The ratio of the cosmic star formation budget hosted by galaxies in the field, groups and clusters is 21:3:1. Morphological ellipticals are minority contributors to local star formation. They make a measurable contribution to the star formation budget only at intermediate-to-high stellar masses, 10.3 < log(M*/M⊙) < 11.2 (where they begin to dominate by number), and typically in the field, where they contribute up to ∼13 per cent of the total star formation budget. This inventory of local star formation serves as a z ∼ 0 baseline that, when combined with similar work at high redshift, will enable us to understand the changes in SFR that have occurred over cosmic time and offers a strong constraint on models of galaxy formation.