The Interstellar Medium of Normal Galaxies: Properties and Evolution \ Part 7 of 7

scientific abstract: we propose to observe an ensemble of atomic and ionic fine structure lines and the infrared continuum to characterize the interstellar medium and the global star formation process in a broad sample of normal galaxies. in this context, normal galaxies are those whose luminosity is dominated by stars and various amounts of ongoing star formation. uniquely suited to the infrared space observatory (iso), these observations will probe the birthsites of stars, yield the physical properties of the gas, dust and radiation field, and refine our picture of the global energetics in galaxies. we propose to study about 70 unresolved galaxies and selected regions of eight nearby, spatially resolved galaxies: ngc 6946, ngc 4449, ic 10, ngc 1313, ngc6744, ngc 2366 or ngc 6822, m101 or ngc 1365 and ngc 4258. we plan to use the lws to probe the warm neutral phase with the cii line at 158 um, and oi at 63 um, and to probe hii regions with nii at 122 um, niii at 57 um, and the oiii lines at 88 and 52 um. we propose to measure with phot the spectral energy distribution of our sources between 100 and 200 um to supplement iras data, and to obtain their images at 7 and 15 um using cam. for the brighter sources, we will also obtain the 312 um spectrum using phts. we plan then to study how these measured and derived physical parameters relate to the global properties of galaxies morphology and kinematics, environment, gas content, metallicity, and star formation efficiency. the ultimate goal of this program is to constrain the evolutionary processes in galaxies, discriminating for example between mechanisms for global star formation activation (cloudcloud collisions or gravitational instability), and suppression (spatial dispersal or photodissociation and heating). normal galaxies account for most of the luminous mass in the local universe. the galaxies we would study sample wide ranges in total luminosi trunc [truncated!, Please see actual data for full text]