The star cluster population of M 51

Free access article

Issue		A&A Volume 431, Number 3, March I 2005


Page(s)		905 - 924
Section		Extragalactic astronomy
DOI		http://dx.doi.org/10.1051/0004-6361:20041078

A&A 431, 905-924 (2005)
DOI: 10.1051/0004-6361:20041078

II. Age distribution and relations among the derived parameters

N. Bastian^{1, 2}, M. Gieles¹, H. J. G. L. M. Lamers^{1, 3}, R. A. Scheepmaker¹ and R. de Grijs⁴

¹ Astronomical Institute, Utrecht University, Princetonplein 5, 3584 CC Utrecht, The Netherlands
e-mail: bastian@astro.uu.nl
² European Astronomical Institute, Karl-Schwarzchild-Strasse 2, 85748 Garching b. München, Germany
³ SRON Laboratory for Space Research, Sorbonnelaan 2, 3584 CA Utrecht, The Netherlands
⁴ Department of Physics & Astronomy, University of Sheffield, Hicks Building, Hounsfield Road, Sheffield S3 7RH, UK

(Received 13 April 2004 / Accepted 25 October 2004 )

Abstract
We use archival Hubble Space Telescope observations of broad-band images from the ultraviolet (F255W-filter) through the near infrared (NICMOS F160W-filter) to study the star cluster population of the interacting spiral galaxy M 51. We obtain age, mass, extinction, and effective radius estimates for 1152 star clusters in a region of ~ $7.3 \times 8.1$ kpc centered on the nucleus and extending into the outer spiral arms. In this paper we present the data set and exploit it to determine the age distribution and relationships among the fundamental parameters (i.e. age, mass, effective radius). We show the critical dependence of the age distribution on the sample selection, and confirm that using a constant mass cut-off, above which the sample is complete for the entire age range of interest, is essential. In particular, in this sample we are complete only for masses above $5\times 10^{4}~M_{\odot}$ for the last 1 Gyr. Using this dataset we find: i) that the cluster formation rate seems to have had a large increase ~50-70 Myr ago, which is coincident with the suggested second passage of its companion, NGC 5195; ii) a large number of extremely young ( <10 Myr) star clusters, which we interpret as a population of unbound clusters of which a large majority will disrupt within the next ~10 Myr; and iii) that the distribution of cluster sizes can be well approximated by a power-law with exponent, $-\eta = -2.2 \pm 0.2$ , which is very similar to that of Galactic globular clusters, indicating that cluster disruption is largely independent of cluster radius. In addition, we have used this dataset to search for correlations among the derived parameters. In particular, we do not find any strong trends between the age and mass, mass and effective radius, nor between the galactocentric distance and effective radius. There is, however, a strong correlation between the age of a cluster and its extinction, with younger clusters being more heavily reddened than older clusters.

Key words: galaxies: individual: M 51 -- galaxies: star clusters

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.