H-alpha kinematics of a z ~ 1 disc galaxy from near-IR integral field spectroscopy

In this letter we present the first 3D spectroscopic study of H-alpha emission in a z ~ 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+/-10 km/s. Combining the 2D map of H-alpha emission with HST F814W imaging, we determine a lower limit of 180+/-20 km/s for the rotation velocity of this M_B(rest) ~ -21 galaxy. We note that our value is significantly higher than the rotation velocity of 120+/-10km/s 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 ~ 1mag 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 ~ 1.