No clear submillimetre signature of suppressed star formation amongst X-ray luminous AGNs. (arXiv:1209.3016v1 [astro-ph.CO])

No clear submillimetre signature of suppressed star formation amongst X-ray luminous AGNs. (arXiv:1209.3016v1 [astro-ph.CO]):
Many theoretical models require powerful active galactic nuclei (AGNs) to
suppress star formation in distant galaxies and reproduce the observed
properties of today's massive galaxies. A recent study based on Herschel-SPIRE
submillimetre observations claimed to provide direct support for this picture,
reporting a significant decrease in the mean star-formation rates (SFRs) of the
most luminous AGNs (Lx>10^44 erg/s) at z=1-3 in the Chandra Deep Field-North
(CDF-N). In this letter we extend these results using Herschel-SPIRE 250um data
in the COSMOS and CDF-S fields to achieve an order of magnitude improvement in
the number of sources at Lx>10^44 erg/s. On the basis of our analyses, we find
no strong evidence for suppressed star formation in Lx>10^44 erg/s AGNs at
z=1-3. The mean SFRs of the AGNs are constant over the broad X-ray luminosity
range of Lx~10^43-10^45 erg/s (with mean SFRs consistent with typical
star-forming galaxies at z~2; <SFRs>~100-200 Msol/yr). We suggest that the
previous CDF-N results were likely due to low number statistics. We discuss our
results in the context of current theoretical models and suggest that it will
be challenging to see the signature of suppressed star formation simply on the
basis of an X-ray luminosity threshold.