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Published March 21, 2014 | Published + Submitted + Supplemental Material
Journal Article Open

The dynamics of isolated Local Group galaxies


We measured velocities of 862 individual red giant stars in seven isolated dwarf galaxies in the Local Group: NGC 6822, IC 1613, VV 124 (UGC 4879), the Pegasus dwarf irregular galaxy (DDO 216), Leo A, Cetus and Aquarius (DDO 210). We also computed velocity dispersions, taking into account the measurement uncertainties on individual stars. None of the isolated galaxies is denser than the densest Local Group satellite galaxy. Furthermore, the isolated dwarf galaxies have no obvious distinction in the velocity dispersion–half-light radius plane from the satellite galaxies of the Milky Way and M31. The similarity of the isolated and satellite galaxies' dynamics and structural parameters imposes limitations on environmental solutions to the 'too big to fail' problem, wherein there are fewer dense dwarf satellite galaxies than would be expected from cold dark matter simulations. This data set also has many other applications for dwarf galaxy evolution, including the transformation of dwarf irregular into dwarf spheroidal galaxies. We intend to explore these issues in future work.

Additional Information

© 2014 The Authors. Published by Oxford University Press on behalf of the Royal Astronomical Society. Accepted 2014 January 6; Received 2013 December 20; in original form 2013 October 31. We are grateful to the many people who have worked to make the Keck Telescopes and their instruments a reality and to operate and maintain the Keck Observatory. The authors wish to extend special thanks to those of Hawaiian ancestry on whose sacred mountain we are privileged to be guests.Without their generous hospitality, none of the observations presented herein would have been possible. We thank Josh Simon and Marla Geha for providing their DEIMOS radial velocity template spectra. We also thank Alan McConnachie and Mike Irwin for sharing their photometric and astrometric catalogue for Cetus. ENK acknowledges support from the Southern California Center for Galaxy Evolution, a multicampus research program funded by the University of California Office of Research, and partial support from NSF grant AST-1009973. JGC thanks NSF grant AST-0908139 for partial support.

Attached Files

Published - MNRAS-2014-Kirby-1015-27.pdf

Submitted - 1401.1208v2.pdf

Supplemental Material - table2.txt


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