A galaxy populations study of a radio-selected protocluster at z~3.1
  We present a population study of several types of galaxies within the
protocluster surrounding the radio galaxy MRC0316-257 at z~3.1. In addition to
the known population of Ly_alpha emitters (LAEs) and [OIII] emitters, we use
colour selection techniques to identify protocluster candidates that are Lyman
break galaxies (LBG) and Balmer break galaxies (BBGs). The radio galaxy field
contains an excess of LBG candidates, with a surface density 1.6\pm0.3 times
larger than found for comparable blank fields. This surface overdensity
corresponds to an LBG volume overdensity of ~8\pm4. The BBG photometric
redshift distribution peaks at the protocluster's redshift, but we detect no
significant surface overdensity of BBG. This is not surprising because a volume
overdensity similar to the LBGs would have resulted in a surface density of
~1.2 that found in the blank field. This could not have been detected in our
sample. Masses and star formation rates of the candidate protocluster galaxies
are determined using SED fitting. These properties are not significantly
different from those of field galaxies. The galaxies with the highest masses
and star formation rates are located near the radio galaxy, indicating that the
protocluster environment influences galaxy evolution at z~3. We conclude that
the protocluster around MRC0316-257 is still in the early stages of formation.
