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Observations of the radio galaxy MRC 0316–257 at and the surrounding field are presented. Using narrow- and broad-band imaging obtained with the VLT, 77 candidate Lyα emitters with a rest-frame equivalent width of >15 Å were selected in a ∼7´´ field around the radio galaxy. Spectroscopy of 40 candidate emitters resulted in the discovery of 33 emission line galaxies of which 31 are Lyα emitters with redshifts similar to that of the radio galaxy, while the remaining two galaxies turned out to be emitters. The Lyα profiles have widths (FWHM) in the range of 120–800 km s-1, with a median of 260 km s-1. Where the signal-to-noise was large enough, the Lyα profiles were found to be asymmetric, with apparent absorption troughs blueward of the profile peaks, indicative of absorption along the line of sight of an mass of at least M. Besides that of the radio galaxy and one of the emitters that is a QSO, the continuum of the emitters is faint, with luminosities ranging from 1.3 L* to M and could be the progenitor of a cluster of galaxies similar to e.g. the Virgo cluster.
Venemans et al. (Wed,) studied this question.