In this letter we present the first 3D spectroscopic study of H \alpha emission in a z \sim 1 field galaxy with an integral field unit .
Using the CIRPASS spectrograph on Gemini-South we map the spatial and velocity distribution of H \alpha emission in the z = 0.819 galaxy CFRS 22.1313 .
We detect two H \alpha emitting regions with a velocity separation of 220 \pm 10 km s ^ { -1 } .
Combining the 2D map of H \alpha emission with HST F814W imaging , we determine a lower limit of 180 \pm 20 km s ^ { -1 } for the rotation velocity of this M _ { B } ( rest ) \sim -21 galaxy .
We note that our value is significantly higher than the rotation velocity of 120 \pm 10km s ^ { -1 } reported by Barden et al .
( 2003 ) for their long-slit spectroscopic study of this galaxy .
Our lower limit on the rotation velocity is entirely consistent with no evolution of the rest B -band Tully-Fisher relation .
The position of this galaxy relative to the mean rest B -band Tully-Fisher relation of Tully & Pierce ( 2000 ) is consistent with brightening of no more than \sim 1 mag at z = 0.8 .
A larger integral field unit sample , without the uncertainties inherent to long-slit samples , is needed to accurately determine the evolution of the Tully-Fisher relation out to z \sim 1 .