Star formation rate and dynamical mass of 10^8 solar mass black hole host galaxies at redshift 6

TL;DR

This study uses ALMA observations to analyze the star formation rates and dynamical masses of z=6 quasar host galaxies with ~10^8 solar mass black holes, revealing lower star formation and comparable [CII]/FIR ratios to local starbursts.

Contribution

It provides new measurements of star formation and dynamical mass for high-redshift quasar hosts, highlighting differences from lower-redshift populations.

Findings

z>6 quasars have lower far-infrared luminosity than lower-redshift counterparts.

[CII]/FIR ratios are similar to local starbursts with comparable star formation rates.

No significant offset from local galaxy relations, but increased scatter at z=6.

Abstract

We present ALMA observations of two moderate luminosity quasars at redshift 6. These quasars from the Canada-France High-z Quasar Survey (CFHQS) have black hole masses of ~10^8 M_solar. Both quasars are detected in the [CII] line and dust continuum. Combining these data with our previous study of two similar CFHQS quasars we investigate the population properties. We show that z>6 quasars have a significantly lower far-infrared luminosity than bolometric-luminosity-matched samples at lower redshift, inferring a lower star formation rate, possibly correlated with the lower black hole masses at z=6. The ratios of [CII] to far-infrared luminosities in the CFHQS quasars are comparable with those of starbursts of similar star formation rate in the local universe. We determine values of velocity dispersion and dynamical mass for the quasar host galaxies based on the [CII] data. We find that there is no significant offset from the relations defined by nearby galaxies with similar black hole masses. There is however a marked increase in the scatter at z=6, beyond the large observational uncertainties.