The post-infall evolution of a satellite galaxy^⋆

¹ Laboratoire d’Astrophysique, École Polytechnique Fédérale de Lausanne (EPFL), 1290 Sauverny, Switzerland
e-mail: matthew.nichols@epfl.ch
² GEPI, Observatoire de Paris, CNRS UMR 8111, Université Paris Diderot, 92125 Meudon Cedex, France

Received: 17 March 2015
Accepted: 11 July 2015

Abstract

We describe a new method that only focuses on the local region surrounding an infalling dwarf in an effort to understand how the hot baryonic halo alters the chemodynamical evolution of dwarf galaxies. Using this method, we examine how a dwarf, similar to Sextans dwarf spheroidal, evolves in the corona of a Milky Way-like galaxy. We find that even at high perigalacticons the synergistic interaction between ram pressure and tidal forces transform a dwarf into a stream, suggesting that Sextans was much more massive in the past to have survived its perigalacticon passage. In addition, the large confining pressure of the hot corona allows gas that was originally at the outskirts to begin forming stars, initially forming stars of low metallicity compared to the dwarf evolved in isolation. This increase in star formation eventually allows a dwarf galaxy to form more metal rich stars compared to a dwarf in isolation, but only if the dwarf retains gas for a sufficiently long period of time. In addition, dwarfs that formed substantial numbers of stars post-infall have a slightly elevated [Mg/Fe] at high metallicity ([Fe/H] ~ −1.5).