Imaging of star clusters in unperturbed spiral galaxies with the Advanced Camera for Surveys - II. A comparison of star cluster systems in five late type spirals

摘要

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: NGC45, NGC1313, NGC4395, NGC5236, and NGC7793. 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 Camera2 (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 600star cluster candidates in the five galaxies, typically spanning ages from 3.9Myr up to 1Gyr and masses from 102up 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