Discovery of six Ly α 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 Lyα emitters with a rest-frame equivalent width of > 20 Å 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 Lyα emitters in radio galaxy protoclusters at z = 4.1, 3.1 and 2.2. The Lyα 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 Lyα emitters occurs at z > 5 and support the idea that radio galaxies pinpoint high density regions in the early Universe.