| Description |
How galaxies convert their gas reservoirs into stars is a stumblingblock in understanding galaxy evolution. The far IR and submm coolinglines arising from photodissociation regions (PDRs) are the keydiagnostics of the interplay between star formation and the evolvingISM throughout the course of the history of the universe. While efforthas been put into physics of PDRs and star formation in the Galaxy andother metal-rich galaxies, little attention has been put intounderstanding the effects of the lower metal abundance on the theseprocesses. Here we propose PACS (CII 158 um, OI 63 um, OI 145um, OIII 88 um, NII 122 um) and SPIRE FTS spectroscopy towardscarefully selected star forming sites in the nearest low metallicitygalaxies, the Magellanic Clouds (MCs) as a benchmark study tocalibrate the primary diagnostics of low metallicity environmentswhich are crucial for ALMA high redshift science. The proximity of theMCs allows Herschel to resolve molecular clouds at 3 pc scale. Ourtargeted regions span a wide diversity of environments, includingdense molecular gas and ionised regions. These new data, together withexisting IRS spectra, Herschel and Spitzer photometry, and a wealth ofgroundbased data including the MAGMA CO data, will allow usto address important unresolved issues: 1) the amount of molecular gashidden in a low extinction phase where CO is photodissociated and thusnot detected; 2) the dependence of the FIR fine structure lines, COexcitation and gas thermodynamics on environment; and 3) the structureof PDRs at low metallicity. Our results will be key to interpretingFIR fine structure lines and CO observations of more distant systems.We will produce PDR models tested at low metallicity, a library of COexcitation at low metallicity, and a calibration of the amount ofCOfree molecular gas as a function of environment. In addition,multiline maps covering the main coolants of the atomic and moleculargas, represent a data product with lasting legacy value. |
