Spatial correlation between submillimetre and Lyman-α galaxies in the SSA 22 protocluster

Lyman-alpha emitters are thought to be young, low-mass galaxies with ages of similar to 10(8) yr (refs 1, 2). An overdensity of them in one region of the sky (the SSA 22 field) traces out a filamentary structure in the early Universe at a redshift of z approximate to 3.1 (equivalent to 15 per cent of the age of the Universe) and is believed to mark a forming protocluster(3,4). Galaxies that are bright at (sub) millimetre wavelengths are undergoing violent episodes of star formation(5-8), and there is evidence that they are preferentially associated with high-redshift radio galaxies(9), so the question of whether they are also associated with the most significant large-scale structure growing at high redshift (as outlined by Lyman-alpha emitters) naturally arises. Here we report an imaging survey of 1,100-mu m emission in the SSA 22 region. We find an enhancement of submillimetre galaxies near the core of the protocluster, and a large-scale correlation between the submillimetre galaxies and the low-mass Lyman-alpha emitters, suggesting synchronous formation of the two very different types of star-forming galaxy within the same structure at high redshift. These results are in general agreement with our understanding of the formation of cosmic structure.