alongside other $z\simeq6$ quasars from the literature [@Willott2017; @Izumi2018; @Izumi2019; @Pensabene2020]. Existing dynamical mass measurements/limits are shown with black errorbars, for NDWFS J1425+3254 [red; @Wang2010], SDSS J2054-0005 [pink; @Pensabene2020] and SDSS J0129-0035 [orange; @Pensabene2020]. Also shown is the $z=0$ relation of @kormendy_2013, for comparison.[]{data-label="fig:BHmassRelation"}](figures/BHmassRelation.pdf)

The Prevalence of Close, Blue Neighbors
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![image](figures/colour_mag.pdf)

Figures \[fig:quasar1\_resids\]–\[fig:quasar3\_resids\] reveal that all of our six quasars have neighboring galaxies within the surrounding $6\farcs5\times6\farcs5$. For SDSS-J0129-0035, NDWFS-J1425+3254 and SDSS-J0005-0006, some companions overlap with the quasar PSF, highlighting the need for the quasar PSF subtraction in order to fully understand the local quasar environment.

The properties of these 20 neighboring galaxies from the maximum posterior model found by are listed in Table \[tab:galaxy\_properties\]. We calculate their UV magnitudes and slopes following the same procedure as for the host galaxies (see Section \[StellarMassLimits\]). The magnitudes and colors of these galaxies are displayed in Figure \[fig:colour\_mag\], along with samples of star-forming galaxies at $z\simeq6$. Four of these companions have colors/UV-slopes that are too red ($\beta>0$) or too blue ($\beta<-4$) to be consistent with $z\simeq6$ galaxies. In addition, seven galaxies are too bright to be likely at this redshift, with magnitudes brighter than $M_{\mathrm{UV}}=-22.1$ mag, the magnitude of the brightest 