Young massive star clusters in nearby galaxies. II. Software tools, data reductions and cluster sizes

A detailed description is given of the data analysis leading to the discovery of young massive star clusters (YMCs) in a sample of 21 nearby galaxies. A new useful tool, ishape, for the derivation of intrinsic shape parameters of compact objects is presented, and some test results are shown. Completeness tests for the cluster samples are discussed, and ishape is used to estimate cluster sizes. Half-light radii of 0-20 pc are derived for clusters in 2 of the most cluster-rich galaxies, NGC 1313 and NGC 5236, which is within the range spanned by globular clusters in the Milky Way and by YMCs in the LMC and some starburst galaxies. Photometric data for all clusters, along with positions and estimated half-light radii, are tabulated. Based on observations made with the Nordic Optical Telescope, operated on the island of La Palma jointly by Denmark, Finland, Iceland, Norway, and Sweden, in the Spanish Observatorio del Roque de los Muchachos of the Instituto de Astrofisica de Canarias, and with the Danish 1.5-m telescope at ESO, La Silla, Chile. Table \ref{tab:clusters} is also available in electronic form at the CDS via anonymous ftp (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.html