The ionized gas in the spiral galaxy NGC 3359 I. Photometry

We combine H alpha imaging and broad-band optical and NIR imaging over the face of the barred galaxy NGC 3359, obtained within the BARS program on the Canary Island telescopes. From the H alpha image we have determined the positions, fluxes, and diamet ers of a total of 547 HII regions, and computed their luminosity function, whose slope is within the range of those of morphologically similar galaxie s found in the literature. We have gone on to quantify other statistical pr operties, such as the diameter distribution and the number density of the H II regions, deduced the global H alpha surface density distribution and dis c scale length and to derive some physical parameters of individual HII reg ions. Measuring the integrated diffuse H alpha flux for the galaxy, we have compared this with the computed ionizing flux escaping from the population of density-bounded HII regions, showing that the latter can give rise to t he diffuse component. We present complementary images in broad-band, and in colours, which give c lues to the star formation and dust distributions, as well as the underlyin g stellar mass distribution. The bar, which shows obvious symptoms of youth , exhibits striking differences in mean position angle as a function of wav elength in the optical and near IR mass component.