Star Formation Histories of Dwarf Spheroidal and Dwarf Elliptical Galaxies in the Local Universe

TL;DR

This study analyzes the star formation histories of early-type dwarf galaxies in the local universe, revealing differences between dwarf spheroidals and ellipticals related to gas retention, feedback, and stellar populations.

Contribution

It provides detailed SFHs of dSphs and dEs, highlighting how their evolutionary paths differ due to gas dynamics and feedback effects, which was not previously well characterized.

Findings

dSphs formed more old, metal-poor stars than dEs.

Reionization and supernova feedback removed gas from dSphs, preventing later star formation.

dEs experienced gas fallback and bursty star formation at later times.

Abstract

We present the star formation histories (SFHs) of early-type dwarf galaxies, dSphs and dEs, in the local universe within z=0.01. The SFHs of early-type dwarf galaxies are characterized by pre-enriched, metal-poor old stellar populations, absence of moderately old stars that have ages of a few Gyr. There are some differences in the SFHs of dSphs and dEs. In particular, dSphs formed old ($\gtrsim10$ Gyr old) metal-poor stars $\sim2$ times more than dEs. The effects of reionization and feedback from supernova explosions are thought to be strong enough to remove the gas left, which prevent moderately old stellar populations in dSphs. In contrast, the ejected gas are not completely removed from dEs and fall back to ignite burst of star formation at a few Gyr after the first period of violent bursts of star formation, showing a suppression of star formation at lookback time $\approx 9.6$ Gyr. The second peak of star formation at lookback time $\approx 4.5$ Gyr in dEs produce moderately old stellar populations. Distinction between dSphs and dEs is useful to examine the SFHS of the early-type dwarfs since the cumulative SFHs are most closely related to their morphology. The stellar mass plays an important role in the SFHs of the early-type dwarfs as a driver of star formation, especially in galaxies with primordial origin.