Life and times of dwarf spheroidal galaxies
S. Salvadori (1), A. Ferrara (1), R. Schneider (2) ((1) Sissa/Isas,, (2) Inaf/Oaa)

TL;DR
This paper presents a cosmological model for dwarf spheroidal galaxy formation, showing they are fossil objects from the pre-reionization era, with most stars formed early and subsequent intermittent star formation cycles, matching observed properties of Sculptor.
Contribution
It introduces an improved semi-analytical model that reproduces the formation, evolution, and observed properties of dSphs within a cosmological context, emphasizing early formation and feedback effects.
Findings
dSphs formed before reionization at z > 6
Most stellar mass formed within 100 Myr after formation
Model matches observed properties of Sculptor dSph
Abstract
We propose a cosmological scenario for the formation and evolution of dwarf spheroidal galaxies (dSphs), satellites of the Milky Way (MW). An improved version of the semi-analytical code GAMETE (GAlaxy Merger Tree & Evolution) is used to follow the dSphs evolution simultaneously with the MW formation, matching the observed properties of both. In this scenario dSph galaxies represent fossil objects virializing at z = 7.2 +/- 0.7 (i.e. in the pre-reionization era z > z_rei = 6) in the MW environment, which at that epoch has already been pre-enriched up to [Fe/H] ~ -3; their dynamical masses are in the narrow range M = (1.6 +/- 0.7) x 10^8 M_sun, although a larger spread might be introduced by a more refined treatment of reionization. Mechanical feedback effects are dramatic in such low-mass objects, causing the complete blow-away of the gas ~100 Myr after the formation epoch: 99% of the…
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