The star-forming progenitors of massive red galaxies

TL;DR

This study uses a semi-analytic model to trace the evolution of star-forming galaxies into massive red galaxies, highlighting the dominant role of cold streams and minor mergers in their star formation history.

Contribution

It demonstrates that most massive red galaxies originate from high-redshift star-forming galaxies, emphasizing the importance of cold streams over major mergers in their evolution.

Findings

90% of today's massive red galaxies were formed through cold streams at z>2

Major mergers are rare but drive extreme starbursts

Two-thirds of red galaxies with recent star formation had merger-triggered events

Abstract

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_Sun 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% of today's red galaxies with M_*>10^11 M_Sun 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.