The fraction of galaxies supported by internal rotation compared to galaxies stabilized by internal pressure provides a strong constraint on galaxy formation models .
In integral field spectroscopy surveys , this fraction is biased because survey instruments typically only trace the inner parts of the most massive galaxies .
We present aperture corrections for the two most widely used stellar kinematic quantities V / \sigma and \lambda _ { R } ( spin parameter proxy ) .
Our demonstration involves integral field data from the SAMI Galaxy Survey and the ATLAS ^ { 3 D } Survey .
We find a tight relation for both V / \sigma and \lambda _ { R } when measured in different apertures that can be used as a linear transformation as a function of radius , i.e. , a first-order aperture correction .
In degraded seeing , however , the aperture corrections are more significant as the steeper inner profile is more strongly affected by the point spread function than the outskirts .
We find that V / \sigma and \lambda _ { R } radial growth curves are well approximated by second order polynomials .
By only fitting the inner profile ( 0.5 R _ { e } ) , we successfully recover the profile out to one R _ { e } if a constraint between the linear and quadratic parameter in the fit is applied .
However , the aperture corrections for V / \sigma and \lambda _ { R } derived by extrapolating the profiles perform as well as applying a first-order correction .
With our aperture-corrected \lambda _ { R } measurements , we find that the fraction of slow rotating galaxies increases with stellar mass .
For galaxies with \log M _ { * } / M _ { \odot } > 11 , the fraction of slow rotators is 35.9 \pm 4.3 percent , but is underestimated if galaxies without coverage beyond one R _ { e } are not included in the sample ( 24.2 \pm 5.3 percent ) .
With measurements out to the largest aperture radius the slow rotator fraction is similar as compared to using aperture corrected values ( 38.3 \pm 4.4 percent ) .
Thus , aperture effects can significantly bias stellar kinematic IFS studies , but this bias can now be removed with the method outlined here .