The physical nature of the 8 o'clock arc based on near-IR IFU spectroscopy with SINFONI

We present an analysis of near-infrared integral field unit spectroscopy for the gravi- tationally lensed Lyman break galaxy, the 8 o'clock arc, taken with SINFONI on the Very Large Telescope. We explore the shape of the spatially-resolved Hprofile and demonstrate that we can decompose it into three main components that partially over- lap (spatially) but are distinguishable when we include the dynamical information. To study the de-lensed morphology of the galaxy we make use of existing B & H imaging from the Hubble Space Telescope and construct a rigorous lens model using a Bayesian grid based lens modeling technique. We apply this lens model to the SINFONI data cube to construct the de-lensed Hline map and the velocity and velocity dispersion maps of the galaxy. We explore the dynamical state of the galaxy and find that the 8 o'clock arc has a complex velocity field that is not simply explained by a single rotating disk. The Hprofile of the galaxy shows a blue-shifted wing suggesting gas outflows of � 200 km s 1 . We confirm previous findings that the 8 o'clock arc lies on the stellar mass-oxygen abundance-star formation rate plane found locally, but it has nevertheless significantly different interstellar medium properties. We show that the gas surface density of the 8 o'clock arc is a factor of 2-4 higher than similar low- redshift galaxies selected from the Sloan Digital Sky Survey. We also find that the electron density in the ionized gas is approximately five times higher than in the com- parison sample, which implies a higher H ii-region pressure as well as likely a higher density interstellar medium than in similar nearby galaxies.