Simple Models of Metal-Line Absorption and Emission from Cool Gas
  Outflows
  We analyze the absorption and emission-line profiles produced by a set of
simple, cool gas wind models motivated by galactic-scale outflow observations.
We implement monte carlo radiative transfer techniques that track the
propagation of scattered and fluorescent photons to generate 1D spectra and 2D
spectral images. We focus on the MgII 2796,28303 doublet and FeII UV1 multiplet
at ~2600A, but the results are applicable to other transitions that trace
outflows (e.g. NaI, Lya, SiII). By design, the resonance transitions show
blue-shifted absorption but one also predicts strong resonance and
fine-structure line-emission at roughly the systemic velocity. This
line-emission `fills-in' the absorption reducing the equivalent width by up to
50%, shift the absorption-lin centroid by tens of km/s, and reduce the
effective opacity near systemic. Analysis of cool gas outflows that ignores
this line-emission may incorrectly infer that the gas is partially covered,
measure asignificantly lower peak optical depth, and/or conclude that gas at
systemic velocity is absent. Because the FeII lines are connected by
optically-thin transitions to fine-structure levels, their profiles more
closely reproduce the intrinsic opacity of the wind. Together these results
naturally explain the absorption and emission-line characteristics observed for
star-forming galaxies at z<1. We also study a scenario promoted to describe the
outflows of z~3 Lyman break galaxies and find prfiles inconsistent with the
observations due to scattered photon emission. Although line-emission
complicates the analysis of absorption-line profiles, the surface brightness
profiles offer a unique means of assessing the morphology and size of
galactic-scale winds. Furthermore, the kinematics and line-ratios offer
powerful diagnostics of outflows, motivating deep, spatially-extended
spectroscopic observations.
