Mergers and the outside-in formation of dwarf spheroidals

A. BENÍTEZ-LLAMBAY, J.F. NAVARRO, M.G. ABADI, S. GOTTLOBER, G. YEPES, Y. HOFFMAN, M. STEINMETZ

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2016

0035-8711

We use a cosmological simulation of the formation of the Local Group to explore the originof age and metallicity gradients in dwarf spheroidal galaxies. We find that a number of simu-lated dwarfs form ?outside-in?, with an old, metal-poor population that surrounds a younger,more concentrated metal-rich component, reminiscent of dwarf spheroidals like Sculptor orSextans. We focus on a few examples where stars form in two populations distinct in age inorder to elucidate the origin of these gradients. The spatial distributions of the two compo-nents reflect their diverse origin; the old stellar component is assembled through mergers, butthe young population forms largely in situ. The older component results from a first episodeof star formation that begins early but is quickly shut off by the combined effects of stellarfeedback and reionization. The younger component forms when a late accretion event addsgas and reignites star formation. The effect of mergers is to disperse the old stellar population,increasing their radius and decreasing their central density relative to the young population.We argue that dwarf-dwarf mergers offer a plausible scenario for the formation of systemswith multiple distinct populations and, more generally, for the origin of age and metallicitygradients in dwarf spheroidals