Based on observations obtained at the European Southern Observatory, Chile [Observing Programme 078.B-0496(B)].
Spatially resolved kinematics of an ultracompact dwarf galaxy★
Version of Record online: 27 APR 2011
© 2011 The Authors Monthly Notices of the Royal Astronomical Society © 2011 RAS
Monthly Notices of the Royal Astronomical Society: Letters
Volume 414, Issue 1, pages L70–L74, June 2011
How to Cite
Frank, M. J., Hilker, M., Mieske, S., Baumgardt, H., Grebel, E. K. and Infante, L. (2011), Spatially resolved kinematics of an ultracompact dwarf galaxy. Monthly Notices of the Royal Astronomical Society: Letters, 414: L70–L74. doi: 10.1111/j.1745-3933.2011.01058.x
- Issue online: 1 JUN 2011
- Version of Record online: 27 APR 2011
- Accepted 2011 April 4. Received 2011 March 30; in original form 2010 December 30
- galaxies: dwarf;
- galaxies: evolution;
- galaxies: kinematics and dynamics;
- galaxies: star clusters
We present the internal kinematics of UCD3, the brightest known ultracompact dwarf galaxy (UCD) in the Fornax cluster, making this the first UCD with spatially resolved spectroscopy. Our study is based on seeing-limited observations obtained with the ARGUS Integral Field Unit of the VLT/FLAMES spectrograph under excellent seeing conditions (0.5–0.67 arcsec FWHM).
The velocity field of UCD3 shows the signature of weak rotation, comparable to that found in massive globular clusters. Its velocity dispersion profile is fully consistent with an isotropic velocity distribution and the assumption that mass follows the light distribution obtained from Hubble Space Telescope imaging. In particular, there is no evidence for the presence of an extended dark matter halo contributing a significant (≳33 per cent within R < 200 pc) mass fraction, nor for a central black hole more massive than ∼5 per cent of the UCD's mass. While this result does not exclude a galaxian origin for UCD3, we conclude that its internal kinematics are fully consistent with it being a massive star cluster.