Journal Article

Kinematic subpopulations in dwarf spheroidal galaxies

Uğur Ural, Mark I. Wilkinson, Andreas Koch, Gerard Gilmore, Timothy C. Beers, Vasily Belokurov, N. Wyn Evans, Eva K. Grebel, Simon Vidrih and Daniel B. Zucker

in Monthly Notices of the Royal Astronomical Society

Published on behalf of The Royal Astronomical Society

Volume 402, issue 2, pages 1357-1368
Published in print February 2010 | ISSN: 0035-8711
Published online February 2010 | e-ISSN: 1365-2966 | DOI: http://dx.doi.org/10.1111/j.1365-2966.2009.15975.x
Kinematic subpopulations in dwarf spheroidal galaxies

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We present new spectroscopic data for 26 stars in the recently discovered Canes Venatici I (CVn I) dwarf spheroidal galaxy, obtained with the Gemini Multi-Object Spectrograph North (GMOS-N) on the Gemini North telescope. We use these data to investigate the recent claim of the presence of two dynamically inconsistent stellar populations in this system. While we find no evidence for kinematically distinct subpopulations in our sample, we also show that the available kinematic data set in CVnI is likely too small to draw robust conclusions about its subpopulations. We are, however, able to obtain a mass estimate for CVn I that is consistent with all available data, including previously published data. We discuss possible differences between our sample and the earlier data set, and study the general detectability of subpopulations in small kinematic samples. We conclude that, in the absence of additional supporting observational evidence (e.g. metallicity gradients), subpopulations in small kinematic samples (typically fewer than 100 stars) should be treated with caution, as their identification depends on multiple parameters and rarely produces a signal at a high confidence level. It is therefore essential to explicitly determine the statistical significance of any suggested subpopulation.

Keywords: stellar dynamics; galaxies: individual: CVn I dSph; galaxies: kinematics and dynamics; Local Group; dark matter

Journal Article.  8909 words.  Illustrated.

Subjects: Astronomy and Astrophysics

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