  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.
