H-alpha survey of M 33 with the six-meter telescope : morphology of the general diffuse emission, evidence for a chaotic medium of bubbles and filaments.

A complete photographic H-alpha survey of M33 has been carried out with the f/1 focal reducer of Courtes (1964, 1972), attached to the prime focus of the 6-m telescope of the Soviet Special Astrophysical Observatory. A list of 748 distinct H II regions has been compiled from the survey photographs. 410 nebulae are newly identified objects. The others were previously cataloged by Boulesteix et al. (1974). The photographs are presented together with identification charts. They reveal an impressive, entirely new appearance for the ionized gas in M33. The 'classical' H II regions are seen bathing in a very chaotic background of H-alpha emission: rings, loops, and arc-shaped and filamentary structures are present everywhere all over the galaxy in and between the arms.