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High Redshift Radio Galaxies (HzRGs) are unique probes of galaxy evolution in the early Universe. They were initially found due to their extreme radio luminosity that makes them potentially detectable to the dawn of time. Observations over the last decade have unequivocally linked HzRGs to the most massive galaxies at high redshifts, harbouring vast stellar populations (Mstar > 1011 MsolarSeymour et al. 2007) as well as extremely active super-massive black holes (SMBHs) at their centres (Drouart et al., 2014). Furthermore, they are commonly found in over-dense, proto-cluster environments (e.g. Mayo et al. 2012 & Galametz et al. 2012) and with huge reservoirs of gas (e.g. Emonts et al., 2016).

Fig 1: The Spiderweb Radio Galaxy at z~2.2, the site of some of the most concentrated star formation in the Universe as well as one of the most powerful super-massive black holes (in terms of accretion and jet power). This activity is thought to be powered by the merger of two massive galaxies. (Image credit: G Miley).

On-going research of this group includes:

  • Searching for the first black holes:

Due to their extreme luminosity, radio-loud SMBHs should be detectable in current and future radio surveys well into the Epoch of Reionisation (6<z<14). We are conducting observations with ALMA and ESO to confirm the high redshift nature of sources selected from the GLEAM survey. Deep ALMA spectroscopic data has been acquired in January 2018 – watch this space!

  • Searching for massive proto-clusters:

The most massive galaxies and most massive/powerful black holes are most likely found in peaks of the dark matter over-densities throughout the Universe. This logic is confirmed by the frequent association of radio galaxies with galaxy over-densities and proto-clusters. For example the Spiderweb Galaxy in Fig. 1 was so named as the preponderance of galaxies around it are akin to flies caught in its gravitational web.

  • HeRGÉ (Herschel Radio Galaxy Evolution) sample:

With our international collaborators we have been studying a sample of 70 HzRGs which have a wealth of multi-wavelength data from X-ray to radio for the last decade. We have found that these powerful radio galaxies are in unique stage of galaxy formation and either have SMBH masses greater than we would expect from M-sigma relation, or are growing at an extreme rate. Currently we are investigating what accretion rates they must have had to produce such extreme radio luminosities.