Top: Continuum-subtracted HeIIλ1640 emission line profile extracted from a $2\stackrel{″}{.}0\times 2\stackrel{″}{.}0$ rectangular aperture centered on the emission peak. The position of the aperture relative to the HeII emission, extracted using a 20 Å wide band is displayed in the top right inset. The orange line corresponds to the modeled emission profile. Bottom: Residuals from the fit, with the dashed orange lines marking the measured noise level.