| Description |
We have shown that SPIRE is capable of exploring high-redshift galaxiesspectroscopically, provided those galaxies are sufficiently bright.Here, we propose to exploit its wide wavelength coverage to study the powerfuldiagnostic rest-frame FIR cooling lines from a sample of 48 bright, lensed - butintrinsically typical - submm galaxies (SMGs). Our targets span 1 < z < 3.1 and 11.5< log L(FIR) < 13.5, and are selected from panoramic Herschel imaging surveys thatare uniquely capable of providing a large, reliable sample at S(350um) > 200mJy, withexcellent ancillary data.We will detect or place sensitive limits on key atomic and ionic cooling lines,e.g. C II, O I, O III, and combine these with ground-based observations of12CO, 13CO, C I and dense-gas tracers to perform a detailed analysis of their ISM andthence understand their energetics and temporal evolution. Using these data we will:1) empirically constrain the interplay between gas cooling and heating in IR galaxies, mapping the evolution of the star-formation efficiency, exploiting our large sample to separate dependencies on L(FIR) and z, and thereby establishing fundamental relationships for the IR galaxy population;2) conclusively address the issue of the contribution of AGN to IR galaxies;3) coadd spectra in the rest frame to delve up to sqrt(48)x deeper than an individual spectrum, to confirm/quantify the signature of powerful feedback via OH molecular outflows, and add powerful diagnostics, e.g. H2O, O I and high-J lines, allowing a complete characterisation of the entire FIR spectrum.Goals 1 and 3 drive the requirement for a sample of 48 SMGs. All our goals requireHerschel and cannot be addressed by other facilities.We stress that the scientific legacy of ISO and Spitzer has in large part been basedon the wealth of data in their spectroscopic archives and the same will likely betrue for Herschel. |
