  We present an analysis of near-infrared integral field unit spectroscopy of
the 8 o'clock arc, a gravitationally lensed Lyman break galaxy, taken with
SINFONI. We explore the shape of the spatially-resolved H\beta\ profile and
demonstrate that we can decompose it into three components that partially
overlap (spatially) but are distinguishable when we include dynamical
information. We use existing B and H imaging from the Hubble Space Telescope to
construct a rigorous lens model using a Bayesian grid based lens modelling
technique. We apply this lens model to the SINFONI data cube to construct the
de-lensed H\beta\ line-flux velocity and velocity dispersion maps of the
galaxy. We find that the 8 o'clock arc has a complex velocity field that is not
simply explained by a single rotating disk. The H\beta\ profile of the galaxy
shows a blue-shifted wing suggesting gas outflows of ~ 200 km s^{-1}. We
confirm that the 8 o'clock arc lies on the stellar mass--oxygen abundance--SFR
plane found locally, but it has nevertheless significantly different gas
surface density (a factor of 2--4 higher) and electron density in the ionized
gas (five times higher) from those in similar nearby galaxies, possibly
indicating a higher density interstellar medium for this galaxy.
