| Description |
High-redshift radio galaxies (HzRGs) are unique markers of the most massive and powerful galaxies in the early Universe, showing signatures of both active galactic nuclei (AGNs) and extreme starbursts. Hence, if the radio-loud AGN phase has a strong effect on the evolution of the host galaxy, it will be most evident in HzRGs. We used Spitzer to carry out a comprehensive survey of 71 HzRGs uniformly covering the redshift range 1<z<5.2. This survey showed that HzRGs have high stellar masses (M>1e11Msun) out to the earliest epochs probed, and mid-infrared AGN luminosities consistent with the most powerful QSOs. To fully understand the evolutionary state of these HzRGs, we now require accurate star formation rates (SFRs), a measurement which is only possible with Herschel. By combining our Spitzer and ground-based sub-millimeter data with five photometric data bands from PACS and SPIRE, we will separate the AGN and star-forming contributions to the total infrared luminosities. Comparing parameters such as specific SFR against AGN power and radio power, and SFR normalised by accretion rate (from the AGN IR luminosity) against radio jet size, we will test theories of how the radio-loud phase stimulates or suppresses star formation (e.g., .feedback.). HzRGs also reside in large dark matter over-densities, and are often found in rich (proto-)clusters. The most efficient SPIRE observing mode provides a five arcminute diameter map, which is well matched to our Spitzer data, thereby allowing environmental studies of the HzRGs. Above z=2, Spitzer and SPIRE colours will allow us to select candidate cluster members with redshifts similar to the HzRG. In total, we request 26.8 hours of PACS and SPIRE imaging of the 62 (out of 71) HzRGs which are not in the ROL. These data will enable us to investigate the interplay between AGN and star-formation activity in the early Universe, which in turn will allow us to test predictions of AGN-driven feedback at this crucial epoch. We will also study the HzRG environments. |
