| Description |
Little is currently known about the dominant mode of star-formation in high-redshift submillimeter-bright galaxies (SMGs), their relation to local ULIRGs and the contribution of AGN to their immense far-infrared (IR) luminosities. Observationally, the physical conditions in these sources are difficult to constrain because the most active regions are also the most highly obscured, and thus can only be probed with mid- and far-IR data. At high redshifts the PACS wavelength coverage is ideally suited to target critical fine structure emission lines from species including oxygen, nitrogen and silicon, and rotational transitions from molecular hydrogen. The relative fluxes of these emission lines, in combination with accurate far-IR luminosities, can be used to constrain the physical conditions in the ISM, such as the density and the ionization state, which in turn provides information about the star-formation triggers and AGN activity. However, most high-redshift galaxies are too faint for these emission lines to be detected, and therefore, studies of the high-redshift ISM are rare. We request Herschel PACS spectroscopy, and 70 and 160um photometry of 13 high-redshift (zvirgul1 to 3), far-IR luminous, gravitationally lensed galaxies. These sources are unique -- the flux boosting from gravitational lensing means that it is feasible to observe them with Herschel, and they all have exceptional ancillary data which complements the proposed program and will maximise the science output from this project. Targets are selected from the H-ATLAS and HerMES surveys and comprise a complete sample of bright lensed SMGs with confirmed CO redshifts. The PACS photometry will constrain the far-IR SEDs, and identify any warm dust (i.e. AGN) components. The spectroscopy will be used to characterize the ISM in these sources, and will double the number of high-redshift galaxies for which such analysis is currently possible. We request a total of 78.9 hours for PACS spectroscopy (73.0 hours) and photometry (5.9 hours) of 13 sources. |
