Physics and Phenomenology of Galactic Starburst Winds

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Cool clouds are expected to be destroyed and incorporated into hot supernova-driven galactic winds. The mass-loading of a wind by the cool medium modifies the bulk velocity, temperature, density, entropy, and abundance profiles of the hot phase relative to an unmass-loaded outflow. We provide general equations and limits for this physics that can be used to infer the rate of cool gas entrainment from X-ray observations, accounting for non-spherical expansion. In general, mass-loading flattens the density and temperature profiles, decreases the velocity and increases the entropy if the Mach number is above a critical value. We first apply this model to a recent high- resolution galactic outflow simulation where the mass-loading can be directly inferred. We show that the temperature, entropy, and composition profiles are well matched, providing evidence that this physics sets the bulk hot gas profiles. We then model the diffuse X-ray emission from the local starburst M82. The non-spherical (more cylindrical) outflow geometry is directly taken from the observed X-ray surface brightness profile. These models predict an asymptotic hot wind velocity of ∼ 1000 km s−1 , which is ∼1.5–2 times smaller than previous predictions. We also show how the observed entropy profile can be used to constrain the outflow velocity, making predictions for future missions like XRISM. We then test the models with 3D hydrodynamic simulations and find that the 1D analytics agree well, and that they are generically stable. As the flow transitions to the subsonic regime, we see the assumptions of a steady-state flow break down, and a multi-phase and multi-dynamical flow is generated through non-linear instabilities.


Mathematical and Physical Sciences: 1st Place (The Ohio State University Edward F. Hayes Graduate Research Forum)


Physics, Astrophysics, Galaxies, Starburst Galaxies, Galaxy Evolution, Hydrodynamics


This paper was presented at the Hayes Graduate Research Forum in 2022 and is related to the following published paper: Dustin D Nguyen, Todd A Thompson, Mass-loading and non-spherical divergence in hot galactic winds: implications for X-ray observations, Monthly Notices of the Royal Astronomical Society, Volume 508, Issue 4, December 2021, Pages 5310–5325,