Dust emission in an accretion-rate-limited sample of z>6 quasars

TL;DR

This study uses ALMA observations to measure dust emission in 27 high-redshift quasars, revealing high star formation rates and dust masses, but no clear correlation between black hole growth and star formation, challenging simple coevolution models.

Contribution

First comprehensive ALMA FIR dust continuum survey of z>6 quasars, providing insights into star formation and dust properties at early cosmic times.

Findings

All quasars detected in FIR emission with high luminosities.

Star formation rates range from 50 to 2700 solar masses per year.

No strong correlation found between quasar UV luminosity and FIR luminosity.

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 < 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).