Supernova Remnants and the Interstellar Medium of M83: Imaging &
  Photometry with WFC3 on HST
  We present Wide Field Camera 3 images taken with the Hubble Space Telescope
within a single field in the southern grand design star-forming galaxy M83.
Based on their size, morphology and photometry in continuum-subtracted
H$\alpha$, [\SII], H$\beta$, [\OIII] and [\OII] filters, we have identified 60
supernova remnant candidates, as well as a handful of young ejecta-dominated
candidates. A catalog of these remnants, their sizes and, where possible their
H$\alpha$ fluxes are given. Radiative ages and pre-shock densities are derived
from those SNR which have good photometry. The ages lie in the range $2.62 <
log(\tau_{\rm rad}/{\rm yr}) < 5.0$, and the pre-shock densities at the blast
wave range over $0.56 < n_0/{\rm cm^{-3}} < 1680$. Two populations of SNR have
been discovered. These divide into a nuclear and spiral arm group and an
inter-arm population. We infer an arm to inter-arm density contrast of 4. The
surface flux in diffuse X-rays is correlated with the inferred pre-shock
density, indicating that the warm interstellar medium is pressurised by the hot
X-ray plasma. We also find that the interstellar medium in the nuclear region
of M83 is characterized by a very high porosity and pressure and infer a SNR
rate of one per 70-150 yr for the nuclear ($R<300 $pc) region. On the basis of
the number of SNR detected and their radiative ages, we infer that the lower
mass of Type II SNe in M83 is $M_{\rm min} = 16^{+7}_ {-5}$ M$_{\odot}$.
Finally we give evidence for the likely detection of the remnant of the
historical supernova, SN1968L.
