EVOLUTION OF DWARF SPHEROIDAL SATELLITES IN THE COMMON SURFACE-DENSITY DARK HALOS

Abstract

ABSTRACT We investigate the growth histories of dark matter halos associated with dwarf satellites in Local Group galaxies and the resultant evolution of the baryonic component. Our model is based on the recently proposed property that the mean surface density of a dark halo inside a radius at maximum circular velocity is universal over a large range of . Given that a surface density of 20 M ⊙ pc−2 well explains dwarf satellites in the Milky Way and Andromeda, we find that the evolution of the dark halo in this common surface-density scale is characterized by the rapid increase of the halo mass assembled by the redshift of the tidal truncation by its host halo, at early epochs of or km s−1. This mass growth of the halo is slow at lower or larger . Taking into account the baryon content in this dark halo evolution, under the influence of the ionizing background radiation, we find that the dwarf satellites are divided into roughly two families: those with km s−1 having high star formation efficiency and those with larger having less efficient star formation. This semianalytical model is in agreement with the high-resolution numerical simulation for galaxy formation and with the observed star formation histories for Fornax and Leo II. This suggests that the evolution of a dark halo may play a key role in understanding star formation histories in dwarf satellites.