| Description |
We propose to study the impact of powerful quasars on the star-forming gas in their host galaxies. central kiloparsec with a 44-hour program using the PACS and SPIRE spectrometers. We are targeting four intrinsically luminous and gravitationally-lensed AGN systems in the zvirgul2-4 era which show evidence of obscured star formation in their hosts. We will measure the five bright far-IR fine-structure transitions: SiII 35, OI 63, OIII 52 & 88, and CII 158 which are the dominant interstellar gas coolants in galaxies. We will combine the Herschel line fluxes with Z-Spec measurements of the peak of the CO spectrum to provide a complete census of the atomic and molecular gas mass and cooling in the central kpc of these systems. Our datasets will allow us to perform two key experiments:1) What heats the gas in the central kpc? When compared with one another and the dust continuum, the line measurements distinguish between UV-photon heating in photo-dissociation regions (PDRs) and bulk heating due to X-rays and/or cosmic rays. Relative to the PDRs, the bulk heating sources are very efficient at heating the gas and produce strong line-to-continuum ratios as well as an enhanced SiII / CII ratio. If X-rays or cosmic rays are really an important heating source, we will see unusually strong SiII and OI in these systems.2) Is the stellar mass function biased toward high masses in these systems? It has been proposed that bulk heating mechanisms are likely to impact the stellar IMF, boosting the characteristic mass by as much as an order of magnitude relative to the Galaxy. Our measurements of the OIII transitions, when compared with the far-IR continuum or CII which trace total star formation provide a measure of the fraction of very massive stars in the stellar IMF. Similarly, comparison of the OIII intensities and lower-ionization species (including upper limits) probe the stellar effective temperature through comparison with nebular models. |
