Alpha element abundances in a LCDM Universe

GARGIULO, IGNACIO; CORA, SOFÍA A.; PADILLA, NELSON D.

Santa Bárbara

Conferencia; KIPT Conference: First Light and Faintest Dwarfs; 2012

Kavli Institute for theoretical physics

We study the chemical enrichment of galaxies using a semi-analytic model of galaxy formation (Cora 2006; Lagos et al. 2008; Tecce et al. 2010), that is combined with a cosmological N-body simulation of dark matter particles. In particular, we track the alpha-element abundances with respect of the iron content of galaxies.  Our aim is to find solutions for two different intriguing trends that are difficult to explain in a build-up scenario of galax formation:   (i) the [alpha/Fe]-Mass relation for elliptical galaxies, that shows an increase in the [alpha/Fe] ratio for more massive galaxies (larger velocity dispersion σ), and (ii) the enhancement of alpha-elements in the Milky Way stellar halo with respect to the corresponding abundances in their satellite galaxies. In order to adress the second we use a simple model for the formation of stellar haloes that considers tidal stripping just before each merger event occurs. Regarding the first problem we found that with a single initial mass function at all epochs the observed trend of [alpha/Fe] with the stellar mass of elliptical galaxies can be hardly reproduced. We propound a top heavy integrated galactic Initial Mass Function (Weidner et al. 2011) as a plausible solution for this problem.