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 MRC 0316-257 at z similar to 3.1. In addition to the known population of Ly alpha emitters 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 +/- 0.3 times larger than found for comparable blank fields. This surface overdensity corresponds to an LBG volume overdensity of similar to 8 +/- 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 similar to 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 spectral energy distribution 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 similar to 3. We conclude that the protocluster around MRC 0316-257 is still in the early stages of formation.