CLUSTERED SUPERNOVAE VERSUS THE GASEOUS DISK AND HALO

Recent developments, both observational and theoretical, require a reevaluation of the effects of clustered supernovae on the two-dimensional porosity parameter Q2D and the rates of mass injection into the halo Ṁ of both cold and hot gas. Theoretically, the effects of the high-|z|, low-density extension of the neutral gas layer have been calculated. Observationally, the distribution of Hα luminosities of extragalactic H II regions has been determined, which allows us to estimate the birthrate of star clusters having N supernovae as a function of N. For the Galaxy, we obtain a Galaxy-wide average Q20 ≈ 0.30, which corresponds to an area filling factor of 0.23, probably close to the true situation. There are two types of bubble. Most clusters produce breakthrough bubbles, which do no more than break through the dense gas disk. But clusters with large N produce enough energy to make blowout bubbles, which blow gas up into the halo. We calculate area filling factors and mass injection rates into the halo for different types of gałaxy. We relate our calculations to two observables, the area covered by H I "holes" and the area covered by giant H II regions. We also discuss the effects of clusters that are too small to produce break-through bubbles, and we reiterate the difficulty of producing the very largest supershells by clustered supernovae.