The growth and assembly of a massive galaxy at z ~ 2
  We study the stellar mass assembly of the Spiderweb Galaxy (MRC 1138-262), a
massive z = 2.2 radio galaxy in a protocluster and the probable progenitor of a
brightest cluster galaxy. Nearby protocluster galaxies are identified and their
properties are determined by fitting stellar population models to their
rest-frame ultraviolet to optical spectral energy distributions. We find that
within 150 kpc of the radio galaxy the stellar mass is centrally concentrated
in the radio galaxy, yet most of the dust-uncorrected, instantaneous star
formation occurs in the surrounding low-mass satellite galaxies. We predict
that most of the galaxies within 150 kpc of the radio galaxy will merge with
the central radio galaxy by z = 0, increasing its stellar mass by up to a
factor of ~ 2. However, it will take several hundred Myr for the first mergers
to occur, by which time the large star formation rates are likely to have
exhausted the gas reservoirs in the satellite galaxies. The tidal radii of the
satellite galaxies are small, suggesting that stars and gas are being stripped
and deposited at distances of tens of kpc from the central radio galaxy. These
stripped stars may become intracluster stars or form an extended stellar halo
around the radio galaxy, such as those observed around cD galaxies in cluster
cores.
