The star-forming progenitors of massive red galaxies

The link between massive red galaxies in the local Universe and star-forming galaxies at high redshift is investigated with a semi-analytic model that has proven successful in many ways, e.g. explaining the galaxy colour-magnitude bimodality and the stellar mass-age relation for red-sequence galaxies. The model is used to explore the processes that drive star formation in different types of galaxies as a function of stellar mass and redshift. We find that most z = 2-4 star-forming galaxies with M * > 10 10 M evolve into red-sequence galaxies. Also, most of the massive galaxies on the red sequence today have passed through a phase of intense star formation at z > 2. Specifically, 90 per cent of today's red galaxies with M * > 10 11 M were fed during this phase by cold streams including minor mergers. Gas-rich major mergers are rare and the effects of merger-driven starbursts are ephemeral. On the other hand, major mergers are important in powering the most extreme starbursts. Gas-rich mergers also explain the tail of intermediate-mass red galaxies that form relatively late, after the epoch of peak star formation. In two-thirds of the currently red galaxies that had an intense star formation event at z < 1, this event was triggered by a merger.