MULTIFREQUENCY WINDOWS ON SPIRAL GALAXIES .1. UBV AND H-ALPHA APERTURE PHOTOMETRY

We present UBV and H-alpha aperture photometry of 78 galaxies in the Coma and Hercules superclusters and in the Cancer cluster. These data are analyzed in conjunction with available measurements forming a sample composed by a variety of environments and spiral types which, although not complete, contains most of the disk galaxies in these regions previously detected in the radio continuum and many objects detected in FIR by IRAS. The optical information provides an estimate of the stellar content and star formation rate (SFR), which are the necessary tools to study the galaxy properties at lower frequencies. No significant differences are found between the average color indices and FIR properties in the clusters and a reference sample of relatively isolated objects. Furthermore, the frequency distributions of the SFR are similar. However, in the cluster A1367 we find that the fraction of actively star forming galaxies is suprisingly large. The data are consistent with the idea that young, high-mass stars are responsible for the dust heating in galaxies with hot FIR colors, but in cooler galaxies the contribution from the general stellar field cannot be ruled out. The nonthermal radio continuum activity in spiral galaxies is found to be proportional to their SFR, but at any given SFR, the radio continuum emissivity is higher in cluster galaxies than in the field. The existence of the strong correlation between the nonthermal radio continuum and thermal FIR fluxes is confirmed, but the ratio of these two quantities is significantly larger in the clusters than in the reference sample.