We present a population study of several types of galaxies within the protocluster surrounding the radio galaxy MRC 0316–257 at z \sim 3.1 .
In addition to the known population of Ly \alpha emitters ( LAEs ) and [ O iii ] 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 \pm 0.3 times larger than found for comparable blank fields .
This surface overdensity corresponds to an LBG volume overdensity of \sim 8 \pm 4 .
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 \sim 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 \sim 3 .
We conclude that the protocluster around MRC 0316–257 is still in the early stages of formation .