Gas shells and magnetic fields in the Orion-Eridanus superbubble
  The Orion-Eridanus superbubble has been blown by supernovae and supersonic
winds of the massive stars in the Orion OB associations. The formation history
and current structure of the superbubble are still poorly understood. It
possibly consists of a combination of nested shells along the line of sight. We
have investigated the composite structure of the Eridanus side of the
superbubble in the light of a new decomposition of the atomic and molecular
gas. We used HI and CO emission lines to separate coherent gas shells in space
and velocity, and we studied their relation to the warm ionised gas probed in
H$\alpha$ emission, to the hot plasma emitting X-rays, and to the magnetic
fields traced by dust polarised emission. We also constrained the relative
distances to the clouds using dust reddening maps and X-ray absorption. We used
the dust polarisation data to estimate the plane-of-sky components of the
magnetic field in several clouds and along the outer rim of the superbubble.
Our gas decomposition has revealed several shells inside the superbubble that
span distances from about 150 pc to 250 pc. One of these shells forms a nearly
complete ring filled with hot plasma. Other shells likely correspond to the
layers of swept-up gas that is compressed behind the expanding outer shock
wave. We used the gas and magnetic-field data downstream of the shock to derive
a shock expansion velocity close to 20 km/s. Taking the X-ray absorption by the
gas into account, we find that the pressure of the hot plasma inside the
superbubble exceeds that in the Local Bubble. It comprises a mix of hotter (3-9
MK) and cooler (0.3-1.2 MK) gas along the lines of sight. The magnetic field
along the western and southern rims and in the approaching wall of the
superbubble appears to be shaped and compressed by the ongoing expansion. We
find plane-of-sky magnetic strengths ranging from 3 to 15 $\mu$G along the rim.
