Dust emission in an accretion-rate-limited sample of z>6 quasars
Abstract
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 < Srest,1900GHz < 5.9mJy, with a median (mean) flux density of 0.88mJy (1.59mJy). The implied FIR luminosities range from LFIR = (0.27-13)x1012 Lsun, with 74% of our quasar hosts having LFIR > 1012 Lsun. The estimated dust masses are Mdust = 107-109 Msun. If the dust is heated only by star formation, then the star formation rates in the quasar host galaxies are between 50 and 2700 Msun/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).
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