We present Keck/DEIMOS spectroscopy of individual stars in the relatively isolated Local Group dwarf galaxies Leo A , Aquarius , and the Sagittarius dwarf irregular galaxy .
The three galaxies—but especially Leo A and Aquarius—share in common delayed star formation histories relative to many other isolated dwarf galaxies .
The stars in all three galaxies are supported by dispersion .
We found no evidence of stellar velocity structure , even for Aquarius , which has rotating H i gas .
The velocity dispersions indicate that all three galaxies are dark matter-dominated , with dark-to-baryonic mass ratios ranging from 4.4 _ { -0.8 } ^ { +1.0 } ( SagDIG ) to 9.6 _ { -1.8 } ^ { +2.5 } ( Aquarius ) .
Leo A and SagDIG have lower stellar metallicities than Aquarius , and they also have higher gas fractions , both of which would be expected if Aquarius were farther along in its chemical evolution .
The metallicity distribution of Leo A is inconsistent with a Closed or Leaky Box model of chemical evolution , suggesting that the galaxy was pre-enriched or acquired external gas during star formation .
The metallicities of stars increased steadily for all three galaxies , but possibly at different rates .
The [ \alpha /Fe ] ratios at a given [ Fe/H ] are lower than that of the Sculptor dwarf spheroidal galaxy , which indicates more extended star formation histories than Sculptor , consistent with photometrically derived star formation histories .
Overall , the bulk kinematic and chemical properties for the late-forming dwarf galaxies do not diverge significantly from those of less delayed dwarf galaxies , including dwarf spheroidal galaxies .