Large scale star formation in galaxies. I. The spirals NGC 7217, NGC 1058 and UGC 12732. Young star groupings in spirals

We present multiband photometric observations of three spiral galaxies selected in a sample suited for the study of young stellar groupings and their relationship with the parent galaxy and the galactic environment. Star forming regions have been identified using an objective technique based on a multivariate statistical analysis. Maps of young star groupings are given for each galaxy. The luminosity functions of the young star group populations show a remarkable similarity with a slope in the range -1.52 to -1.33. The size distributions peak around the classical 100 pc value of the Local Group associations for two out of the three galaxies. NGC 1058 shows smaller associations (peak at ~ 50 pc). The total number of young groups per unit B absolute luminosity of the galaxy is significantly greater in UGC 12732. The activity of star formation is in all three galaxies clearly stronger in the central regions. Tables~1, 2, 3 are only available in electronic form at the CDS via anonymous ftp to cdsarc.u-strasbg.fr (130.79.128.5) or via http://cdsweb.u-strasbg.fr/Abstract.htm