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tokens: of 27 or 23 kpc. Figure 3. Left: radial profiles of the (blue) and continuum (red) emission. Error bars with colors matching the points indicate the error in the weighted mean, and larger gray error bars indicate the dispersion of individual spaxels in the image. Only points with >3 σ detections are shown. Gray triangles show the radial profile of a quasar observed on the same nights as BX418, and the dotted gray line shows the best-fit Moffat profile to the quasar data. Blue lines indicate exponential fits as described in the text. Right: growth curve for the total flux as a function of radius. The horizontal blue line shows the total flux measured as described in the text. We also show the azimuthally averaged profile of a quasar that was observed on the same nights as BX418, with exposures alternating with those of BX418 (gray triangles, where the peak value has been scaled to match the peak continuum surface brightness of BX418). The radial profile of the quasar is reasonably well-fit with a Moffat profile with FWHM = 096 (dotted gray line), and we use this profile as a model of the PSF. As this model is a nearly perfect match to the continuum profile of BX418, we conclude that the continuum emission is not resolved; given the half-light radius of 1.5 kpc from HST imaging (Erb et al. 2010 ), this is not surprising. We then fit the binned surface profile with an exponential function convolved with the PSF (solid blue line), finding a best-fit scale length of 2.58 ± 0.02 kpc; however, this model fits only the inner portion of the extended halo, significantly underestimating the surface brightness at radii greater than 18 (15 kpc). Fitting an exponential function to only the points beyond this radius (dashed blue line), we find a scale length of 6.2 ± 1.1 kpc. This scale length of 6.2 kpc lies at the low end of the scale lengths found for stacked images at z > 2, which range from ∼7 to ∼25 kpc (Steidel et al. 2011 ; Momose et al. 2014 , 2016 ); these measurements are also made at radii ≳2′′. It is also within the range of halo scale lengths found for individual galaxies detected by the Multi Unit Spectroscopic Explorer (MUSE; Leclercq et al. 2017 ). In the right panel of Figure 3 we show the growth curve for the flux as a function of radius, with the total flux measured as described above indicated by the horizontal blue line. This curve indicates that half of the observed emission lies within a radius of 7.1 kpc (08), and the flux reaches 95% of its total value at a radius of 23 kpc (28). 3.2. The Velocity Structure of Extended <inline-formula> <tex-math> </tex-math> <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="apjlaacff6ieqn68.gif"></inline-graphic> </inline-formula> Emission Examination of the profiles of individual spaxels within the extended halo reveals significant differences in the blue-to-red peak ratio and velocity separation in different regions. We show two examples in Figure 4 . In the left and right