Star Formation Histories of Early-type Dwarfs in Group Environment

Abstract We investigate the star formation histories (SFHs) of 983 early-type dwarf galaxies classified into five morphological subtypes-dS0, dE, dEbc, dSph, and dEbl-across six environments ranging from the field to rich clusters such as Ursa Major and Virgo. Using full spectral fitting of SDSS spectra with the starlight code, we derive detailed SFHs and chemical enrichment patterns. We find that SFHs are primarily shaped by morphology, with environment playing a secondary but non-negligible role. Red early-type dwarfs (dS0, dE, dSph) typically formed most of their stars early and quenched rapidly, whereas blue early-type dwarfs (dEbc, dEbl) exhibit extended or ongoing star formation and host extremely metal-poor stars, suggesting continued pristine gas accretion. Environmental dependence is clearest in low-mass systems: field galaxies often show prolonged SFHs and delayed enrichment, while Virgo Cluster galaxies tend to quench earlier and enrich more rapidly. Cumulative SFHs reinforce these trends, with dSph galaxies showing the earliest quenching and least environmental dependence, indicating a likely primordial origin. Metallicity evolution also varies with mass and environment, progressing most slowly in low-mass field galaxies and most rapidly in high-mass cluster galaxies. Our results highlight the combined influence of morphology, stellar mass, and environment on the evolutionary diversity of early-type dwarfs, and suggest that both internal processes (nature) and external conditions (nurture) are intricately linked in shaping their star formation and chemical enrichment histories.