2004A&A...424....1D

We present a 1.2mm (250GHz) map obtained with MAMBO on the IRAM 30m telescope of the central 25arcmin² of the proto-cluster surrounding the z=4.1 radio galaxy TN J1338-1942. The map reaches a 1σ sensitivity of 0.6mJy in the central area, increasing to 1.2mJy at the edges. We detect 10 candidate mm sources, of which 8 are also detected in a deep VLA 1.4GHz map and/or a VLT R-band image. Three sources have a flux density S_1.2mm>4.0mJy, representing a 7σ overdensity compared to random field surveys, which predict only 1 such source in our map area. We obtained SCUBA/JCMT 850µm and 450µm photometry of six radio/optically identified MAMBO sources, confirming 5 of them with S/N>4. Radio-to-mm and mm-to-submm redshift estimators cannot put strong constraints on the redshifts of these MAMBO sources, but 9 of them are consistent within the uncertainties (mean Δz=+2.6) with z=4.1. One faint MAMBO source is possibly identified with an extremely red object (R-K=6.1) at a likely spectroscopic redshift z=1.18. The four brightest MAMBO sources are all located north of the radio galaxy, while the densest area of companion Lyα excess and Lyman break galaxies is to the southeast. None of the 14 spectroscopically confirmed Lyα emitters in the MAMBO field are detected at 1.2mm; their average 1.2mm flux density is <S_1.2mm≥0.25±0.24mJy. If the mm sources lie at z=4.1, none of them show excess Lyα emission in our narrow-band images. Both populations thus show no apparent overlap, possibly due to dust quenching the Lyα emission. If the mm sources are part of the proto-cluster, our results suggest that galaxies with star formation rates of a few 1000M_☉/yr^ could be spread throughout the proto-cluster over projected scales of at least 2Mpc.