Mapping UV Properties Throughout the Cosmic Horseshoe: Lessons from
  VLT-MUSE
  We present the first spatially-resolved rest-frame UV study of the
gravitationally lensed galaxy, the 'Cosmic Horseshoe' (J1148+1930) at z=2.38.
Our gravitational lens model shows that the system is made up of four
star-forming regions, each ~4-8 kpc^2 in size, from which we extract four
spatially exclusive regional spectra. We study the interstellar and wind
absorption lines, along with CIII] doublet emission lines, in each region to
investigate any variation in emission/absorption line properties. The mapped
CIII] emission shows distinct kinematical structure, with velocity offsets of
~+/-50 km/s between regions suggestive of a merging system, and a variation in
equivalent width that indicates a change in ionisation parameter and/or
metallicity between the regions. Absorption line velocities reveal a range of
outflow strengths, with gas outflowing between -200<v(km/s)<-50 relative to the
systemic velocity of that region. Interestingly, the strongest gas outflow
appears to emanate from the most diffuse star-forming region. The
star-formation rates remain relatively constant (~8-16 M_sol/yr), mostly due to
large uncertainties in reddening estimates. As such, the outflows appear to be
'global' rather than 'locally' sourced. We measure electron densities with a
range of log(Ne)=3.92-4.36 cm^-3, and point out that such high densities may be
common when measured using the CIII] doublet due to its large critical density.
Overall, our observations demonstrate that while it is possible to trace
variations in large scale gas kinematics, detecting inhomogeneities in physical
gas properties and their effects on the outflowing gas may be more difficult.
This study provides important lessons for the spatially-resolved rest-frame UV
studies expected with future observatories, such as JWST.
