Herschel Extreme Lensing Line Observations openParHELLOclosePar

We request 59.8 hours of Herschel time to observe 20 normal starforming galaxies in the CII 158 micron and OI 63 micron lines. These galaxies lie at high redshift (1<z<3). They are highly magnified by gravitational lensing, but have modest star formation rates. Therefore they represent our best chance of studying star formation and the interstellar medium in typical, common galaxies at this epoch.Redshift 1 to 3 spans the peak of both star formation activity and black hole accretion in active galactic nuclei a period that was crucial inshaping our modern universe. Most of this redshift range is inaccesible to groundbased observations of CII, OI, or both.Herschel offers the unique opportunity to study both lines with high sensitivity throughout this epoch (using HIFI for CII and PACS for OI).These two lines are the main cooling lines of the atomic medium.By measuring their fluxes, we will measure (1) the cooling efficiency of gas, (2) gas densities and temperatures near starforming regions, and (3) gas pressures, which are important to drive the windsthat provide feedback to starformation processes.By combining the proposed observations with existing multiwavelength data on these objects, we will obtain as complete a picture of galaxyscale star formation and ISM physical conditions at high redshifts as we have at z0. Then perhaps we can understand why star formation and AGN activity peaked at this epoch.In Herschel cycle OT1, 49 high redshift IR luminous galaxies were approved for spectroscopy, but only two socalled normal galaxies were included. This is an imbalance that should be corrected, to balance Herschel.s legacy. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]