Dust emission in an accretion-rate-limited sample of z>6 quasars
  We present Atacama Large Millimeter Array 1mm observations of the rest-frame
far-infrared (FIR) dust continuum in 27 quasars at redshifts 6.0 < z < 6.7. We
detect FIR emission at >3sigma in all quasar host galaxies with flux densities
at ~1900GHz in the rest-frame of 0.12 < S_rest,1900GHz < 5.9mJy, with a median
(mean) flux density of 0.88mJy (1.59mJy). The implied FIR luminosities range
from L_FIR = (0.27-13)x10^12 L_sun, with 74% of our quasar hosts having L_FIR >
10^12 L_sun. The estimated dust masses are M_dust = 10^7-10^9 M_sun. If the
dust is heated only by star formation, then the star formation rates in the
quasar host galaxies are between 50 and 2700 M_sun/yr. In the framework of the
host galaxy-black hole coevolution model a correlation between ongoing black
hole growth and star formation in the quasar host galaxy would be expected.
However, combined with results from the literature to create a
luminosity-limited quasar sample, we do not find a strong correlation between
quasar UV luminosity (a proxy for ongoing black hole growth) and FIR luminosity
(star formation in the host galaxy). The absence of such a correlation in our
data does not necessarily rule out the coevolution model, and could be due to a
variety of effects (including different timescales for black hole accretion and
FIR emission).
