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Chemistry and kinematics of the late-forming dwarf irregular galaxies Leo A, Aquarius, and the Sagittarius DIG

Citation

Kirby, EN and Rizzi, L and Held, EV and Cohen, JG and Cole, AA and Manning, EM and Skillman, ED and Weisz, DR, Chemistry and kinematics of the late-forming dwarf irregular galaxies Leo A, Aquarius, and the Sagittarius DIG, Astrophysical Journal, 834, (1) Article 9. ISSN 0004-637X (2017) [Refereed Article]


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Copyright Statement

© 2016. The American Astronomical Society.

DOI: doi:10.3847/1538-4357/834/1/9

Abstract

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 (SFHs) 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 further 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 [α/Fe] ratios at a given [Fe/H] are lower than that of the Sculptor dwarf spheroidal galaxy, which indicates more extended SFHs than Sculptor, consistent with photometrically derived SFHs. 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.

Item Details

Item Type:Refereed Article
Keywords:galaxies: dwarf, Local Group, stars: abundances
Research Division:Physical Sciences
Research Group:Astronomical and Space Sciences
Research Field:Galactic Astronomy
Objective Division:Expanding Knowledge
Objective Group:Expanding Knowledge
Objective Field:Expanding Knowledge in the Physical Sciences
Author:Cole, AA (Dr Andrew Cole)
Author:Manning, EM (Miss Ellen Manning)
ID Code:115360
Year Published:2017
Deposited By:Mathematics and Physics
Deposited On:2017-03-20
Last Modified:2017-04-07
Downloads:30 View Download Statistics

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