The dynamical mass of the young cluster W3 in NGC 7252

Free access article

Issue		A&A Volume 416, Number 2, March III 2004


Page(s)		467 - 473
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20031604

A&A 416, 467-473 (2004)
DOI: 10.1051/0004-6361:20031604

Heavy-weight globular cluster or ultra compact dwarf galaxy?

C. Maraston¹, N. Bastian^{2, 3}, R. P. Saglia⁴, M. Kissler-Patig², F. Schweizer⁵ and P. Goudfrooij⁶

¹ Max-Planck-Institut für Extraterrestrische Physik, Giessenbachstraße, 85748 Garching b. München, Germany
² European Southern Observatory, Karl-Schwarzschild-Str. 2, 85748 Garching, Germany
³ Astronomical Institute, Utrecht University Princetonplein 5, 3584 CC Utrecht, The Netherlands
⁴ Universitäts-Sternwarte München, Scheinerstr. 1, 81679 München, Germany
⁵ Carnegie Observatories, 813 Santa Barbara Str., Pasadena, CA 91101-1292, USA
⁶ Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA

(Received 6 June 2003 / Accepted 2 October 2003 )

Abstract
We have determined the dynamical mass of the most luminous stellar cluster known to date, i.e. object W3 in the merger remnant galaxy NGC 7252. The dynamical mass is estimated from the velocity dispersion measured with the high-resolution spectrograph UVES on VLT. Our result is the astonishingly high velocity dispersion of $\sigma=45 \pm 5~{\rm km\,s^{-1}}$ . Combined with the large cluster size $R_{\rm eff}=17.5 \pm 1.8~{\rm pc}$ , this translates into a dynamical virial mass for W3 of $(8 \pm 2) \times 10^7 \ensuremath{M_{\odot}}$ . This mass is in excellent agreement with the value (~ $7.2\times 10^7~\ensuremath{M_{\odot}}$ ) we previously estimated from the cluster luminosity ( $M_{\rm V}=-16.2$ ) by means of stellar M/L ratios predicted by Simple Stellar Population models (with a Salpeter IMF) and confirms the heavy-weight nature of this object. This results points out that the NGC 7252-type of mergers are able to form stellar systems with masses up to ~ $10^8~\ensuremath{M_{\odot}}$ . We find that W3, when evolved to ~10 Gyr, lies far from the typical Milky Way globular clusters, but appears to be also separated from $\omega$ Cen in the Milky Way and G1 in M 31, the most massive old stellar clusters of the Local Group, because it is too extended for a given mass, and from dwarf elliptical galaxies because it is much more compact for its mass. Instead the aged W3 is amazingly close to the compact objects named ultracompact dwarf galaxies (UCDGs) found in the Fornax cluster (Hilker et al. 1999; Drinkwater et al. 2000), and to a miniature version of the compact elliptical M 32. These objects start populating a previously deserted region of the fundamental plane.

Key words: galaxies: star clusters -- galaxies: individual: NGC 7252 -- stars: fundamental parameters

Offprint request: C. Maraston, maraston@mpe.mpg.de

SIMBAD Objects

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access. An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
You can define your own OpenURL resolver with your EDPS Account. In this case your choice will be given priority over that of your library.
You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.