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Published May 20, 2012 | Erratum + Accepted Version + Published
Journal Article Open

The Dynamics and Metallicity Distribution of the Distant Dwarf Galaxy VV124


VV124 (UGC 4879) is an isolated, dwarf irregular/dwarf spheroidal (dIrr/dSph) transition-type galaxy at a distance of 1.36 Mpc. Previous low-resolution spectroscopy yielded inconsistent radial velocities for different components of the galaxy, and photometry hinted at the presence of a stellar disk. In order to quantify the stellar dynamics, we observed individual red giants in VV124 with the Keck/DEIMOS spectrograph. We validated members based on their positions in the color-magnitude diagram, radial velocities, and spectral features. Our sample contains 67 members. The average radial velocity is = −29.1 ± 1.3 km s^(−1), in agreement with the previous radio measurements of H I gas. The velocity distribution is Gaussian, indicating that VV124 is supported primarily by velocity dispersion inside a radius of 1.5 kpc. Outside that radius, our measurements provide only an upper limit of 8.6 km s^(−1) on any rotation in the photometric disk-like feature. The velocity dispersion is σ_v = 9.4± 1.0 km s^(−1), from which we inferred a mass of M_(1/2) = (2.1 ± 0.2)× 10^7 M_⊙ and a mass-to- light ratio of (M/L_V)_(1/2) = 5.2 ± 1.1 M_⊙/L_⊙, both measured within the half-light radius. Thus, VV124 contains dark matter. We also measured the metallicity distribution from neutral iron lines. The average metallicity, <[Fe/H]> = −1.14 ± 0.06, is consistent with the mass-metallicity relation defined by dwarf spheroidal galaxies. The dynamics and metallicity distribution of VV124 appear similar to dSphs of similar stellar mass.

Additional Information

© 2012 The American Astronomical Society. Received 2011 December 14; accepted 2012 March 19; published 2012 May 3. 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. We are grateful to the many people who have worked to make the Keck Telescope and its 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 Marla Geha for providing radial velocity template spectra observed with DEIMOS and for her generous assistance in measuring radial velocities. We also thank the referee for a detailed report that greatly improved this manuscript. Support for this work was provided by NASA through Hubble Fellowship grant 51256.01 awarded to ENK by the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., for NASA, under contract NAS 5-26555. JGC thanks NSF grant AST-0908139 for partial support. Facility: Keck:II (DEIMOS)

Attached Files

Published - 0004-637X_751_1_46.pdf

Accepted Version - 1203.4561

Erratum - 0004-637X_768_1_96.pdf


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