We have shown that Herschel is capable of exploring high-redshift galaxies spectroscopically, provided those galaxies are sufficiently bright. Here, we propose to exploit the wide wavelength coverage of the SPIRE FTS to study the powerful diagnostic rest-frame FIR cooling lines from a unique and complete sample of 25 bright, gravitationally-lensed - but intrinsically typical - submm galaxies (SMGs). We can thus perform the first detailed analysis of their ISM, tracing their density structure and searching 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 a good range of L(FIR) (12 < 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 the key atomic 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 model their ISM and thence understand 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 I]145.5, 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 goals require Herschel and cannot be addressed by other facilities. We stress that the scientific legacy of ISO and Spitzer has in large part been based on the wealth of data in their s...pectroscopic archives and the same is likely to be true for Herschel.
Publication
The Herschel SPIRE Fourier Transform Spectrometer Spectral Feature Finder - II. Estimating radial velocity of SPIRE spectral observation sources . Scott Jeremy P. et al. . Monthly Notices of the Royal Astronomical Society . null . null . 2020MNRAS.496.4894S , A surprising consistency between the far-infrared galaxy luminosity functions of the field and Coma . Hickinbottom S. et al. . Monthly Notices of the Royal Astronomical Society, Volume 442, Issue 2, p.1286-1293 . 442 . 10.1093/mnras/stu924 . 2014MNRAS.442.1286H , The Herschel SPIRE Fourier Transform Spectrometer Spectral Feature Finder - III. Line identification and off-axis spectra . Benson Chris S. et al. . Monthly Notices of the Royal Astronomical Society . null . null . 2020MNRAS.496.4906B , Stacked Average Far-infrared Spectrum of Dusty Star-forming Galaxies from the Herschel-SPIRE Fourier Transform Spectrometer . Wilson Derek et al. . The Astrophysical Journal, Volume 848, Issue 1, article id. 30, 31 pp. (2017). . 848 . 10.3847/1538-4357/aa8cc7 . 2017ApJ...848...30W , Far-infrared Herschel SPIRE spectroscopy of lensed starbursts reveals physical conditions of ionized gas . Zhang Zhi-Yu et al. . Monthly Notices of the Royal Astronomical Society, Volume 481, Issue 1, p.59-97 . 481 . 10.1093/mnras/sty2082 . 2018MNRAS.481...59Z , Herschel reveals a molecular outflow in a z = 2.3 ULIRG . George R. D. et al. . Monthly Notices of the Royal Astronomical Society, Volume 442, Issue 2, p.1877-1883 . 442 . 10.1093/mnras/stu967 . 2014MNRAS.442.1877G , The Herschel SPIRE Fourier Transform Spectrometer Spectral Feature Finder I. Th...e Spectral Feature Finder and Catalogue . Hopwood R. et al. . Monthly Notices of the Royal Astronomical Society . null . null . 2020MNRAS.496.4874H ,
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.
