Probing the Interstellar Medium of ULIRGs/SMGs at high redshift

Early results from Herschel have shown we are entering a newand exciting era in the study of the interstellar media of galaxies.Using the farinfrared cooling lines, we have demonstrated thecapability of the PACS spectrometer in deep integrations reachingline sensitivities of 3 sigma sensitivities of 3e18 W/m/m in <virgul2 hours exposures on resolved lines, reaching as low as1e18 W/m/m in virgul7 hours with the red detector allowing us toprobe the ISM of galaxies in place at the peak of starformationand AGN activity in the Universe (Sturm et al. 2010). This proposalbuilds on these first studies by performing PACS spectroscopy of asample of bright and strongly lensed infrared/submm galaxies atmoderate to high redshift. By virtue of the magnification due tolensing we are able to probe intrinsically lower luminosity galaxieswhich would normally be beyond the reach of the Herschel spectrometers, and, for the first time, constrain the physical processes andstate of the ISM in these highredshift galaxies. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]