Changes of the Star Formation Rate and the Initial Mass Function with Galactic Radius

Abstract

Using the data of a survey of the northern part of the galactic plane at far infrared wavelengths (71–95 μm and 114–195 μm) made with a balloon born instrument (Gispert, Puget and Serra, 1981) we can compute the far infrared luminosity of the galactic plane as a function of galactic radius. The result is shown in Figure 1. The far infrared radiation is stellar light reemitted by dust, and is a good measure of the total energy output. The ratio of the far infrared luminosity to the amount of interstellar gas gives a measure of the star formation rate per unit mass of interstellar gas. Furthermore one can compute the “infrared excess” (ratio of the infrared luminosity to the energy in Lyman a photons in H II regions). The number of Lyman continuum photons is evaluated by taking the number of Lyman continuum photons from giant H II regions from Smith et al., 1978 and assuming that the fraction of Lyman continuum photons coming from giant H II regions is constant throughout the galaxy.