Abstract
We exploit ALMA 870um 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-alpha haloes (often termed Ly-alpha blobs:
LABs). Three of the AGNs are detected by ALMA and have implied SFRs of
~220-410~M_sun/yr; the non detection of the other five AGNs places SFR upper
limits of <210 M_sun/y. The mean SFR of the protocluster AGNs (~110-210
M_sun/yr) is consistent (within a factor of ~0.7-2.3) with that found for
co-eval AGNs in the field, implying that galaxy growth is not significantly
accelerated across the protocluster environment. However, when also considering
ALMA data from the literature, we find some evidence for significantly elevated
mean SFRs (up-to a factor of ~4.3 over the field) for the AGNs at the
protocluster core. We also show that all of the four protocluster LABs are
associated with an ALMA counterpart within the extent of their Ly-alpha
emission. The SFRs of the ALMA sources within the LABs (~150-410 M_sun/yr) are
consistent with those expected for co-eval massive star-forming galaxies in the
field. Furthermore, the two giant LABs (with physical extents of >100 kpc) do
not host more luminous star formation than the smaller LABs, despite being an
order of magnitude brighter in Ly-alpha emission. We use these results to
discuss star formation as the power source of LABs.
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