Rapid Coeval Black Hole and Host Galaxy Growth in MRC 1138-262: The
  Hungry Spider
  We present a detailed study of the infrared spectral energy distribution of
the high-redshift radio galaxy MRC 1138-26 at z = 2.156, also known as the
Spiderweb Galaxy. By combining photometry from Spitzer, Herschel and LABOCA we
fit the rest-frame 5-300 um emission using a two component, starburst and
active galactic nucleus (AGN), model. The total infrared (8 - 1000 um)
luminosity of this galaxy is (1.97+/-0.28)x10^13 Lsun with (1.17+/-0.27) and
(0.79+/-0.09)x10^13 Lsun due to the AGN and starburst components respectively.
The high derived AGN accretion rate of \sim20% Eddington, and the measured star
formation rate (SFR) of 1390pm150 Msun/yr, suggest that this massive system is
in a special phase of rapid central black hole and host galaxy growth, likely
caused by a gas rich merger in a dense environment. The accretion rate is
sufficient to power both the jets and the previously observed large outflow.
The high SFR and strong outflow suggest this galaxy could potentially exhaust
its fuel for stellar growth in a few tens of Myr, although the likely merger of
the radio galaxy with nearby satellites suggest bursts of star formation may
recur again on time scales of several hundreds of Myr. The age of the radio
lobes implies the jet started after the current burst of star formation, and
therefore we are possibly witnessing the transition from a merger-induced
starburst phase to a radio-loud AGN phase. We also note tentative evidence for
[CII]158um emission. This paper marks the first results from the Herschel
Galaxy Evolution Project (Project HeRGE), a systematic study of the
evolutionary state of 71 high redshift, 1 < z < 5.2, radio galaxies.
