  We exploit the gravitational potential of massive cluster lenses to probe the
emission line properties of six z=1 galaxies which appear as highly magnified
luminous arcs. Using the GMOS integral field spectrograph together with
detailed cluster lens models we reconstruct the intrinsic morphologies and
two-dimensional velocity fields in these galaxies on scales corresponds to
\~0.5kpc (unlensed) at z=1. Four of the galaxies have stable disk-like
kinematics, whilst the other two resemble interacting or starburst galaxies.
These galaxies lie close to the mean rest-frame I-band Tully-Fisher relation
for nearby spirals suggesting a clear preference for hierarchical growth of
structure. In the rest-frame B-band, the observations suggest 0.5+/-0.3mag of
brightening, consistent with increased star-formation activity at z=1. However,
the galaxies with stable disk kinematics have more slowly rising rotation
curves than expected from galaxies with similar surface brightness in the local
Universe. We suggest that this may arise because the distant galaxies have
lower bulge masses than their local counter-parts. Whilst this study is based
on only six galaxies, the gain in flux and in spatial resolution achieved via
gravitational magnification provides a much more detailed view of the high
redshift Universe than possible with conventional surveys.
