| Description |
We have shown that Herschel is capable of exploring high-redshift galaxiesspectroscopically, provided those galaxies are sufficiently bright.Here, we propose to exploit the wide wavelength coverage of the SPIRE FTSto study the powerful diagnostic rest-frame FIR cooling lines from a uniqueand complete sample of 25 bright, gravitationally-lensed - butintrinsically typical - submm galaxies (SMGs). We can thus perform the firstdetailed analysis of their ISM, tracing their density structure andsearching for variations in line strengths compared to local counterparts.Our targets span 1 < z < 3.1 (where C II is not accessible to ALMA) and agood range of L(FIR) (12 < log L(FIR) < 13.5), and are selected frompanoramic Herschel imaging surveys that are uniquely capable of providing alarge, reliable sample at S(350um) > 200mJy, with excellent ancillary data.We will detect or place sensitive limits on the key atomic 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 model their ISM and thenceunderstand their energetics and evolution. Using these data we will:1) map the evolution of the gas content as a function of redshift, via the sensitivity of C II/L(FIR) to M(H2);2) search for changes in the properties of the star-forming gas as a function of redshift and L(FIR);3) coadd the spectra in the rest frame to delve up to 5x deeper still, to search for faint lines, e.g. H2O and O I145.5, allowing a complete characterisation of the average emission;4) conclusively address the issue of the contribution of AGN to the immense luminosities of submm galaxies.Goals 1-3 drive the requirement for a sample of 25 SMGs. All our goalsrequire Herschel and cannot be addressed by other facilities.We stress that the scientific legacy of ISO and Spitzer has in large partbeen based on the wealth of data in their spectroscopic archives and thesame is likely to be true for Herschel. |
