We present detailed images of diffuse UV intergalactic light ( IGL ) , situated in a 60 kpc 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 , synchrotron self-Compton emission and scattering of galactic stellar light as possible sources of the IGL .
Dust scattered quasar light is an unlikely possibility that can not 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 \pm 8 \hbox { $ \thinspace M _ { \odot } $ } { \thinspace yr } ^ { -1 } .
Within 70 kpc 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 .