Lyman-\alpha absorption beyond the disk of simulated spiral galaxies
  We present an analysis of the origin and properties of the circum-galactic
medium (CGM) in a suite of 11 cosmological zoom simulations resembling present
day spiral galaxies. On average the galaxies retain about 50\% of the cosmic
fraction in baryons, almost equally divided into disc (interstellar medium)
gas, cool CGM gas and warm-hot CGM gas. At radii smaller than 50 kpc the CGM is
dominated by recycled warm-hot gas injected from the central galaxy, while at
larger radii it is dominated by cool gas accreted onto the halo. The recycled
gas typically accounts for one-third of the CGM mass. We introduce the novel
publicly available analysis tool \textsc{pygad} to compute ion abundances and
mock absorption spectra. For Lyman-${\alpha}$ absorption we find good agreement
of the simulated equivalent width (EW) distribution and observations out to
large radii. Disc galaxies with quiescent assembly histories show significantly
more absorption along the disc major axis. By comparing the EW and HI column
densities we find that CGM Lyman-${\alpha}$ absorbers are best represented by
an effective line-width $b\approx 50 - 70$ km s$^{-1}$ that increases mildly
with halo mass, larger than typically assumed.
