Hα kinematics of a z~ 1 disc galaxy from near-infrared integral field spectroscopy

In this Letter we present the first 3D spectroscopic study of Hα emission in a z~ 1 field galaxy with an integral field unit. Using the Cambridge Infrared Panoramic Survey Spectrograph (CIRPASS) on Gemini-South, we map the spatial and velocity distribution of Hα emission in the z= 0.819 galaxy CFRS 22.1313. We detect two Hα emitting regions with a velocity separation of 220 +/- 10 kms^-1. Combining the 2D map of Hα emission with Hubble Space Telescope F814W imaging, we determine a lower limit of 180 +/- 20 kms^-1 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 +/- 10 kms^-1 reported by Barden et al. 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 Pierce & Tully 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 determine the evolution of the Tully-Fisher relation accurately out to z~ 1.