additional quasar SDSS J0005-0006. Other $z>5.6$ quasars with sub-mm observations are plotted in gray [@fan_2000; @fan_2001; @fan_2003; @fan_2004; @Fan2006; @petric_2003; @bertoldi_2003; @mahabal_2005; @Cool2006; @mcgreer_2006; @goto_2006; @venemans_2007; @venemans_2013; @Wang2007; @Wang2008; @Wang2011; @Wang2013; @Kurk2007; @kurk_2009; @willott_2007; @willott_2010; @willott_2010b; @jiang_2007; @jiang_2008; @jiang_2009; @mortlock_2009; @mortlock_2011; @zeimann_2011; @DeRosa2011; @de_rosa_2014; @omont_2013; @Banados2014; @wu_2015]. []{data-label="fig:submm_selection"}](figures/FIRvsFUV.pdf){width="\columnwidth"}

Although the FIR emission suggests the presence of significant dust in the host galaxies, the quasar discovery spectra (rest-frame UV) do not show anomalous features compared to the rest of the population— they are otherwise normal quasars, rather than showing significant spectral reddening or absorption features such as present in the FIRST/2MASS sample at lower redshifts [@Urrutia2008; @Glikman2015]. Furthermore, more than $\sim25\%$ of quasars have similarly high FIR luminosities [@willott_2007; @Wang2008; @Wang2010; @Wang2011], so these FIR-luminous quasars are broadly representative of a significant sub-population, rather than atypical objects.

Dust-Free Quasar
----------------

In addition to the FIR-luminous quasars described above, we also analyze data from the prototype hot-dust-free quasar [@fan_2004; @jiang_2010], which also lacks cold dust [@Wang2008]. With a lower-luminosity and no evidence for significant dust content, this quasar was selected as a counterpoint to . This source is representative of a smaller, but still important sub-population. At $5.8<z<6.4$, @jiang_2010 found two apparently 