unique insights into the connection between black hole and galaxy growth at the end of the Epoch of Reionization [@Shields2006; @Wang2013; @Valiante2014; @Schulze2014; @Willott2017].

The extreme nature of these objects, with large black hole masses [$M_{\rm BH}\simeq10^9M_\odot$; @Barth2003; @Jiang2007; @Kurk2007; @DeRosa2011] and accretion rates near and even above the Eddington limit [@willott_2010; @DeRosa2011], suggests that these quasars may live in extreme high-density environments. However, observations do not find that quasars reside in high-density regions [e.g. @Kim2009; @Banados2013; @Morselli2014], challenging our understanding. Theoretically, however, it is kpc-scale interactions that could trigger supermassive black hole growth [e.g., @Sanders1988; @Hopkins2006], despite not universally being observed in lower redshift ($z<2$) quasar systems [@Cisternas2011; @Kocevski2012; @Mechtley2016; @Villforth2018; @Marian2019]. Recently, Atacama Large Millimeter/submillimeter Array (ALMA) observations in the sub-mm have detected galaxies around high-redshift quasars at separations of $\sim8$–60 kpc [@Decarli2017; @Trakhtenbrot2017], which have been interpreted as major galaxy interactions. These observations suggest that major mergers may be important drivers of rapid black hole growth in the early Universe, and thus observations must probe the local environments of quasars to understand these extreme systems.

Alongside their local environment, many studies investigate the host galaxies of these quasars to understand the connection between black hole and galaxy 