Discovery of six Lyα emitters near a radio galaxy at z∼5.2

We present the results of narrow-band and broad-band imaging with the Very Large Telescope* of the field surrounding the radio galaxy TN J0924-2201 at z = 5.2. Fourteen candidate Lyalpha emitters with a rest-frame equivalent width of >20 Angstrom were detected. Spectroscopy of 8 of these objects showed that 6 have redshifts similar to that of the radio galaxy. The density of emitters at the redshift of the radio galaxy is estimated to be a factor 1.5-6.2 higher than in the field, and comparable to the density of Lya emitters in radio galaxy protoclusters at z = 4.1, 3.1 and 2.2. The Lyalpha emitters near TN J0924-2201 Could therefore be part of a structure that will evolve into a massive cluster. These observations confirm that substantial clustering of Lyalpha emitters occurs at z > 5 and support the idea that radio galaxies pinpoint high density regions in the early Universe.