ALMA observations of a $z$ ≈ 3.1 Protocluster: Star Formation from Active Galactic Nuclei and Lyman-Alpha Blobs in an Overdense Environment

We exploit ALMA 870 µm observations to measure the star-formation rates (SFRs) of eight X-ray detected Active Galactic Nuclei (AGNs) in a z ≈ 3.1 protocluster, four of which reside in extended Ly α haloes (often termed Ly α blobs: LABs). Three of the AGNs are detected by ALMA and have implied SFRs of ≈ 220–410 M⊙ yr−1 ; the non detection of the other five AGNs places SFR upper limits of ∼ 100 kpc) do not host more luminous star formation than the smaller LABs, despite being an order of magnitude brighter in Ly α emission. We use these results to discuss star formation as the power source of LABs.