First results from SMAUG: Characterization of Multiphase Galactic
  Outflows from a Suite of Local Star-Forming Galactic Disk Simulations
  Large scale outflows in star-forming galaxies are observed to be ubiquitous,
and are a key aspect of theoretical modeling of galactic evolution in a
cosmological context, the focus of the SMAUG (Simulating Multiscale
Astrophysics to Understand Galaxies) project. Gas blown out from galactic
disks, similar to gas within galaxies, consists of multiple phases with large
contrasts of density, temperature, and other properties. To study multiphase
outflows as emergent phenomena, we run a suite of ~pc-resolution local galactic
disk simulations using the TIGRESS framework. Explicit modeling of the
interstellar medium (ISM), including star formation and self-consistent
radiative heating plus supernova feedback, regulates ISM properties and drives
the outflow. We investigate the scaling of outflow mass, momentum, energy, and
metal loading factors with galactic disk properties, including star formation
rate (SFR) surface density (\Sigma_SFR~10^{-4}-1 M_sun/kpc^2/yr), gas surface
density (~1-100 M_sun/pc^2), and total midplane pressure (or weight)
(~10^3-10^6 k_B cm^{-3} K). The main components of outflowing gas are
mass-delivering cool gas (T~10^4 K) and energy/metal-delivering hot gas (T~10^6
K). Cool mass outflow rates measured at outflow launch points (one or two scale
heights) are 1-100 times the SFR (decreasing with \Sigma_SFR), although in
massive galaxies most mass falls back due to insufficient outflow velocity. The
hot galactic outflow carries mass comparable to 10% of the SFR, together with
10-20% of the energy and 30-60% of the metal mass injected by SN feedback. The
characteristic outflow velocities of both phases scale very weakly with SFR, as
v_out \propto \Sigma_SFR^{0.1~0.2}, consistent with observations. Importantly,
our analysis demonstrates that in any physically-motivated cosmological wind
model, it is crucial to include at least two distinct thermal wind components.
