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 dataset from the SDSS to first study how the star-formation budget in galaxies with stellar masses greater than $\log ({\text{M}}_{\ast }/{\text{M}}_{\odot })=10$ 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 $z<0.075$ ($\sim$65 per cent) takes place in spiral galaxies, that reside in the field, and have stellar masses between $10<\log ({\text{M}}_{\ast }/{\text{M}}_{\odot })<10.9$. 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, $10.3<\log ({\text{M}}_{\ast }/{\text{M}}_{\odot })<11.2$ (where they begin to dominate by number), and typically in the field, where they contribute up to $\sim$13 per cent of the total star-formation budget. This inventory of local star formation serves as a $z\sim 0$ baseline which, 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.

9 pages, 4 figures, MNRAS in press