II. A comparison of star cluster systems in five late type spirals
Departamento de Física y Astronomía, Facultad de Ciencias, Universidad de Valparaíso. Av. Gran Bretaña 1111, Valparaíso, Chile e-mail: firstname.lastname@example.org
2 Astronomical Institute, University of Utrecht, Princetonplein 5, 3584 CC, Utrecht, The Netherlands e-mail: S.S.Larsen@uu.nl
3 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany e-mail: email@example.com
4 UCO/Lick Observatory, University of California, Santa Cruz, CA 95064, USA e-mail: firstname.lastname@example.org
5 Universidad de Concepción, Departamento de Astronomía. Casilla 160-C, Concepción, Chile e-mail: email@example.com
Accepted: 3 February 2009
Aims. Our goal is to investigate the formation of star clusters in relatively unperturbed environments. To do this, we studied the five nearby spiral galaxies: NGC 45, NGC 1313, NGC 4395, NGC 5236, and NGC 7793.
Methods. We obtained images of the galaxies and their star cluster systems in using the Advanced Camera for Surveys (ACS) and the Wide Field Planetary Camera 2 (WFPC2) on board the Hubble Space Telescope. From a comparison of the broad-band colours with simple stellar population (SSP) models, we derived individual properties for each galaxy for the clusters such as masses, ages, and sizes, as well as global star cluster system properties such as the age distribution, luminosity function, and disruption time for clusters.
Results. We identified about 600 star cluster candidates in the five galaxies, typically spanning ages from 3.9 Myr up to 1 Gyr and masses from 102 up to 105 . We used the cluster age distribution to reconstruct the recent star formation history of each galaxy and observed significant variations from galaxy to galaxy. We went on to derive the luminosity function of the young star clusters and found slopes around (similar to the ones found in previous studies) and the brightest star cluster magnitudes consistent with a random sampling of the luminosity function without involving an upper luminosity cut off. Finally, the sample includes only a handful of old globular clusters in each galaxy from which we derive low globular cluster specific frequencies.
Key words: galaxies: star clusters / galaxies: photometry
Based on observations made with the NASA/ESA Hubble Space Telescope, obtained at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-26555. These observations are associated with programme # 9774.
© ESO, 2009