A Search for clusters at high redshift I.: Candidate Lyα emitters near 1138-262 at z=2.2

Radio, optical and X-ray observations of the powerful radio galaxy PKS 1138-262 at z = 2.156 have suggested that this galaxy is a massive galaxy in the center of a forming cluster. We have imaged 1138-262 and the surrounding 38 square arcminute field with the Very Large Telescope(a) in a broad band and a narrow band encompassing the redshifted Ly alpha emission. We detect 50 objects with rest equivalent width larger than 20 Angstrom and a luminous, highly extended Ly alpha halo around 1138-262. If the radio galaxy is at the center of a forming cluster, as observations at other wavelengths suggest, these objects are candidate Ly alpha emitting cluster galaxies.