The Role of Feedback in Shaping the Structure of the Interstellar Medium
  We present an analysis of the role of feedback in shaping the neutral
hydrogen (HI) content of simulated disc galaxies. For our analysis, we have
used two realisations of two separate Milky Way-like (~L*) discs - one
employing a conservative feedback scheme (MUGS), the other significantly more
energetic (MaGICC). To quantify the impact of these schemes, we generate zeroth
moment (surface density) maps of the inferred HI distribution; construct power
spectra associated with the underlying structure of the simulated cold ISM, in
addition to their radial surface density and velocity dispersion profiles. Our
results are compared with a parallel, self-consistent, analysis of empirical
data from THINGS (The HI Nearby Galaxy Survey). Single power-law fits
(P~k^gamma) to the power spectra of the stronger-feedback (MaGICC) runs (over
spatial scales corresponding to 0.5 kpc to 20 kpc) result in slopes consistent
with those seen in the THINGS sample (gamma = -2.5). The weaker-feedback (MUGS)
runs exhibit shallower power law slopes (gamma = -1.2). The power spectra of
the MaGICC simulations are more consistent though with a two-component fit,
with a flatter distribution of power on larger scales (i.e., gamma = -1.4 for
scales in excess of 2 kpc) and a steeper slope on scales below 1 kpc (gamma =
-5), qualitatively consistent with empirical claims, as well as our earlier
work on dwarf discs. The radial HI surface density profiles of the MaGICC discs
show a clear exponential behaviour, while those of the MUGS suite are
essentially flat; both behaviours are encountered in nature, although the
THINGS sample is more consistent with our stronger (MaGICC) feedback runs.
