The H\alpha emission of the spiral galaxy NGC 7479

Abstract

We use the catalogue of HII regions obtained from a high quality continuum-subtracted H$\alpha$ image of the grand design spiral galaxy NGC 7479, to construct the luminosity function (LF) for the HII regions (over 1000) of the whole galaxy. Although its slope is within the published range for spirals of the same morphological type, the unusually strong star formation along the intense bar of NGC 7479 prompted us to analyze separately the HII regions in the bar and in the disc. We have calculated the physical properties of a group of HII regions in the bar and in the disc selected for their regular shapes and absence of blending. We have obtained galaxy-wide relations for the HII region set: diameter distribution function and also the global H$\alpha$ surface density distribution. As found previously for late-type spirals, the disc LF shows clear double-linear behaviour with a break at log L$_{H\alpha}$=38.6 (in erg/s). The bar LF is less regular. This reflects a physical difference between the bar and the disc in the properties of their populations of regions.