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Chemistry and Kinematics of the Late-Forming Dwarf Irregular Galaxies Leo A, Aquarius, and Sagittarius DIG

Kirby, Evan N. and Rizzi, Luca and Held, Enrico V. and Cohen, Judith G. and Cole, Andrew A. and Manning, Ellen M. and Skillman, Evan D. and Weisz, Daniel R. (2017) Chemistry and Kinematics of the Late-Forming Dwarf Irregular Galaxies Leo A, Aquarius, and Sagittarius DIG. Astrophysical Journal, 834 (1). Art. No. 9. ISSN 0004-637X. doi:10.3847/1538-4357/834/1/9.

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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 Type:Article
Related URLs:
URLURL TypeDescription Paper
Kirby, Evan N.0000-0001-6196-5162
Rizzi, Luca0000-0003-0882-2327
Cohen, Judith G.0000-0002-8039-4673
Cole, Andrew A.0000-0003-0303-3855
Weisz, Daniel R.0000-0002-6442-6030
Additional Information:© 2016. The American Astronomical Society. Received 2016 September 27; revised 2016 October 24; accepted 2016 October 26; published 2016 December 22. We thank Alan McConnachie, Nobuo Arimoto, and Mike Irwin for kindly sharing their photometry catalog for Aquarius. We also thank Yazan Momany and his collaborators for sharing their photometry catalog of SagDIG. Deidre Hunter provided kind assistance with the LITTLE THINGS 21 cm images. We acknowledge support from the National Science Foundation through grant 1614081. Facility: Keck:II (DEIMOS) - . The data presented herein were obtained at the W. M. Keck Observatory, which is operated as a scientific partnership among the California Institute of Technology, the University of California, and the National Aeronautics and Space Administration. The Observatory was made possible by the generous financial support of the W. M. Keck Foundation.
Group:Astronomy Department
Funding AgencyGrant Number
W. M. Keck FoundationUNSPECIFIED
Subject Keywords:galaxies: abundances; galaxies: dwarf; galaxies: individual (Leo A, DDO 210, Sgr dIG) ; Local Group; stars: abundances
Issue or Number:1
Record Number:CaltechAUTHORS:20170213-151130703
Persistent URL:
Official Citation:Evan N. Kirby et al 2017 ApJ 834 9
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:74266
Deposited By: George Porter
Deposited On:13 Feb 2017 23:37
Last Modified:11 Nov 2021 05:25

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