High Redshift Radio Galaxies: Laboratories for Massive Galaxy and
  Cluster Formation in the early Universe
  High redshift radio galaxies are among the largest, most luminous, most
massive, and most beautiful objects in the Universe. They are generally
identified from their radio emission, thought to be powered by accretion of
matter onto supermassive black holes in the nuclei of their host galaxies.
Observations show that they are energetic sources of radiation throughout most
of the electromagnetic spectrum, including relativistic plasma, gas and dust,
stars and the active galactic nuclei (AGN). 1 HzRGs are inferred to be
extremely massive, including old stars (up to $\sim$ 10$^{12}$ M$_{\odot}$),
hot gas (up to $\sim$ 10$^{12}$ M$_{\odot}$) and molecular gas (up to $\sim$
10$^{11}$ M$_{\odot}$).Because they are highly luminous and (unlike quasars)
spatially resolvable from the ground, most components of HzRGs provide
important diagnostic information about the spatial distributions of processes
within HzRGs and their environment. The fact that the different constituents
are present in the same objects and that the {\bf {\it interrelationships and
interactions between them}} can be studied make distant radio galaxies unique
laboratories for probing massive galaxy and cluster formation in the early
Universe.
