The Interstellar Medium of Star-forming Irregular Galaxies: The View with ISO

Astrophys.J.553:121-145,2001 We present mid-infrared imaging and far-infrared (FIR) spectroscopy of 5 IBm galaxies observed by ISO as part of our larger study of the inter- stellar medium of galaxies. Most of the irregulars in our sample are very actively forming stars. The mid-infrared imaging was in a band centered at 6.75 microns that is dominated by polycyclic aromatic hydrocarbons (PAHs) and in a band centered at 15 microns that is dominated by small dust grains. The spectroscopy of 3 of the galaxies includes [CII]158 microns and [OI]63 microns, important coolants of photodissociation regions (PDRs), and [OIII]88 microns and [NII]122 microns, which come from ionized gas. [OI]145 microns and [OIII]52 microns were measured in one galaxy as well. These data are combined with PDR and HII region models to deduce properties of the interstellar medium of these galaxies.