Herschel Spectroscopic Survey of Far-Infrared Fine Structure Lines in intermediate redshift Ultraluminous Infrared Galaxies

Herschel has provided unprecedented insight into the properties of the ISM of local Ultraluminous Infrared Galaxies (ULIRGs) andhigh redshift submillimetre bright galaxies. Although matched in luminosity the ISM properties of the two samples are markedly different.We propose to exploit the wide wavelength coverage of SPIREFTS to study farinfrared fine structure cooling lines from a unique sample of 23 intermediate redshift ULIRGs. Our targets span the redshift range 0.2 < z < 0.8 and luminosity range 12 < log L(IR) < 13 and have been selected from the Herschel Multitiered Extragalactic Survey (HerMES) with excellent ancillarydata. The redshift range has been chosen so that we can simultaneously detect key cooling lines CII 158 microns, NII 205 microns and CI 371 microns in all of our targets. Our sample is suitably selected to link the properties of the ISM near and far: it is at theseintermediate redshifts where the change in the properties of the ISM takes place. Using the proposed observations we will:1) investigate the properties of the ISM of ULIRGs at a redshift where they contribute dominantly to the total IR energy density;2) search for changes in the ISM as a function of luminosity and redshift; 3) explore metallicities (through CII/NII ratio) and investigate the validity of NII as a star formation indicator; 4) address the effect of the AGN in the surrounding ISM.To complete our goals we request observations for a sample of 23 ULIRGs. Herschel is currently the only facility capable of addressing these important questions. truncated!, Please see actual data for full text [truncated!, Please see actual data for full text]