paper

The significant contribution of minor mergers to the cosmic star formation budget

arXiv:1310.0007 · doi:10.1093/mnrasl/slt136

Abstract

We estimate an empirical lower limit for the fraction of cosmic star formation that is triggered by minor mergers in the local Universe. Splitting the star-formation budget by galaxy morphology, we find that early-type galaxies (ETGs) host ~14% of the budget, while Sb/Sc galaxies host the bulk (~53%) of the local star formation activity. Recent work indicates that star formation in nearby ETGs is driven by minor mergers, implying that at least ~14% of local star formation is triggered by this process. A more accurate estimate can be derived by noting that an infalling satellite likely induces a larger starburst in a galaxy of 'later' morphological type, both due to higher availability of gas in the accreting galaxy and because a bigger bulge better stabilizes the disk against star formation. This enables us to use the star formation in ETGs to estimate a lower limit for the fraction of star formation in late-type galaxies (LTGs) that is minor-merger-driven. Using a subsample of ETGs that is mass and environment-matched to the LTGs (implying a similar infalling satellite population), we estimate this limit to be ~24%. Thus, a lower limit for the fraction of cosmic star formation that is induced by minor mergers is ~35% (14% [ETGs] + 0.24 x 86% [LTGs]). The observed positive correlation between black hole and galaxy mass further implies that a similar fraction of black hole accretion may also be triggered by minor mergers. Detailed studies of minor-merger remnants are therefore essential, to quantify the role of this important process in driving stellar mass and black hole growth in the local Universe.

MNRAS Letters in press

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