A comprehensive photometric study of circumnuclear star-forming rings

We present photometry in U, B, V, R and I continuum bands and in H alpha and H beta emission lines for a sample of 336 circumnuclear star-forming regions located in early-type spiral galaxies with different levels of activity in their nuclei. They are nearby galaxies, with distances less than 100 Mpc, 60 per cent of which are considered as interacting objects. This survey of 20 nuclear rings aims to provide insight into their star formation properties as age, stellar population and star formation rate. Extinction-corrected Ha luminosities range from 1.3 x 10(38) to 4 x 10(41) erg s(-1), with most of the regions showing values between 39.5 <= logL(H alpha) <= 40, which implies masses for the ionizing clusters higher than 2 x 10(5) M-circle dot. H alpha and H beta images have allowed us to obtain an accurate measure of extinction. We have found an average value of A(V) = 1.85 mag. (U - B) colour follows a two maximum distribution around (U - B) similar or equal to -0.7, and -0.3; (R - I) also presents a bimodal behaviour, with maximum values of 0.6 and 0.9. Reddest (U - B) and (R - I) regions appear in non-interacting galaxies. Reddest (R - I) regions lie in strongly barred galaxies. For a significant number of H II regions, the observed colours and equivalent widths are not well reproduced by single burst evolutionary theoretical models.

A comprehensive photometric study of circumnuclear star-forming rings - I. The sample Articles