We have shown that SPIRE is capable of exploring high-redshift galaxies spectroscopically, provided those galaxies are sufficiently bright.
Here, we propose to exploit its wide wavelength coverage to study the powerful diagnostic rest-frame FIR cooling lines from a sample of 48 bright, lensed - but intrinsically 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 that are uniquely capable of providing a large, reliable sample at S(350um) > 200mJy, with excellent 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 of 12CO, 13CO, C I and dense-gas tracers to perform a detailed analysis of their ISM and thence 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 require Herschel and cannot be addressed by other facilities.
We stress that the scientif...ic legacy of ISO and Spitzer has in large part been based on the wealth of data in their spectroscopic archives and the same will likely be true for Herschel.
Herschel was launched on 14 May 2009! It is the fourth 'cornerstone' mission in the ESA science programme. With a 3.5 m Cassegrain telescope it is the largest space telescope ever launched. It is performing photometry and spectroscopy in approximately the 55-671 µm range, bridging the gap between earlier infrared space missions and groundbased facilities.
European Space Agency, 2013, Characterising The Ism Of Bright Comma Lensed Star-Forming Galaxies Across Cosmic Time With The Spire Fts, SPG v14.2.0, European Space Agency, https://doi.org/10.5270/esa-5g9vuc9
