Résumé / Abstract Journal-club_Galaxies

Journal-club Galaxies

« (2) Massive early-type galaxies: the last 12 billion years »

Sugata Kaviraj

I review our current understanding of the formation of massive early-type galaxies (ETGs), in the context of survey-based studies that dominate the modern galaxy evolution effort. Recent work leveraging the rest-frame UV (e.g. using GALEX at low z and optical HST surveys at intermediate z) have put unprecedented constraints on ETG evolution since z~1. While the bulk of the stars in ETGs are indeed old, these studies indicate widespread star formation in these systems, that creates ~20% of their stellar mass at z<1, via repeated minor mergers between ETGs and gas-rich dwarfs.
While these UV studies have quantified the late-epoch (z<1) evolution of ETGs, surprisingly little is known about exactly when and how the dominant (~80%), old stars in these galaxies formed. This requires a survey-scale UV-optical study of primordial ETGs in the early Universe, which is only now becoming possible. Exploiting new HST-WFC3 near-infrared imaging and existing HST-ACS optical imaging in GOODS-South, I present a statistical empirical study of primordial ETGs at the epoch of peak cosmic star formation(z~1-3). I show that the stellar mass assembly in ETGs peaks in the redshift range 2-5 (with a median value of z~3), over short timescales (<1 Gyr), largely independent of the galaxy stellar mass. Around 50% of these primordial SGs do not build their stars via major mergers, and those that have experienced a recent major merger show only marginally bluer colours and mild enhancements in specific star formation rate of ~20%. This points (empirically) to processes other than major mergers (e.g. minor mergers, cold streams) as the dominant channel of mass assembly in primordial ETGs and, by extension, the assembly of the old stellar populations that dominate today's Universe.
jeudi 22 mars 2012 - 11:30
Salle 281, Institut d'Astrophysique
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