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Massive early-type galaxies : the last 10 billion years

Sugata Kaviraj

While early-type galaxies (ETGs) are traditionally considered to be old passively-evolving systems which formed their stars in the early Universe via major mergers, the recent literature is dramatically altering our understanding of how these galaxies have formed and evolved over time. Using recent UV data I demonstrate that ETGs host widespread star formation that creates 20-30% of their stellar mass after z 1, via repeated minor mergers with gas-rich dwarfs. Surveys using the HST’s WFC3 camera are allowing unprecedented access to ETGs at high redshift. By exploiting such data I show that at least 50% of ETGs do not build their bulk stellar mass via major mergers, which suggests that other processes (e.g. minor mergers, direct cold accretion) are the dominant channel of mass assembly in primordial ETGs and, by extension, the assembly of the old stellar populations that dominate today’s Universe.