  We present detailed images of diffuse UV intergalactic light (IGL), situated
in a 60kpc halo that surrounds the radio galaxy MRC 1138-262 at z=2. We discuss
the nature of the IGL and rule out faint cluster galaxies, nebular continuum
emission, synchrotron, inverse Compton emission and scattering of galactic
stellar light as possible sources of the IGL. Dust scattered quasar light is an
unlikely possibility that cannot be ruled out entirely. We conclude that the
source of the IGL is most likely to be a young stellar population distributed
in a halo encompassing the radio and satellite galaxies, undergoing star
formation at a rate greater than 57 Msun/yr. Within 70kpc of the radio core,
approximately 44% of the star formation that is traced by UV light occurs in
this diffuse mode. The average UV colour of the IGL is bluer than the average
galaxy colour, and there is a trend for the IGL to become bluer with increasing
radius from the radio galaxy. Both the galaxies and the IGL show a UV
colour--surface brightness relation which can be obtained by variations in
either stellar population age or extinction. These observations show a
different, but potentially important mode of star formation, that is diffuse in
nature. Star formation, as traced by UV light, occurs in two modes in the high
redshift universe: one in the usual Lyman break galaxy clump-like mode on kpc
scales, and the other in a diffuse mode over a large region surrounding massive
growing galaxies. Such a mode of star formation can easily be missed by high
angular resolution observations that are well suited for detecting high surface
brightness compact galaxies. Extrapolating from these results, it is possible
that a significant amount of star formation occurs in large extended regions
within the halos of the most massive galaxies forming at high redshift.
