Dynamics of hot galactic winds launched from spherically-stratified starburst cores

TL;DR

This paper generalizes the classic galactic wind model to non-uniform energy and mass injection profiles, revealing new flow behaviors and providing predictions for observable spectral signatures in starburst regions.

Contribution

It introduces a family of solutions for spherically-symmetric galactic winds with non-uniform injection, extending the CC85 model and analyzing their physical and observational implications.

Findings

Flow maintains constant Mach number for certain injection profiles.

Interior flow velocity is approximately 41% of the asymptotic velocity.

Spectral predictions differ between uniform and non-uniform models, testable by future X-ray telescopes.

Abstract

The analytic galactic wind model derived by Chevalier and Clegg in 1985 (CC85) assumes $\textit{uniform}$ energy and mass-injection within the starburst galaxy nucleus. However, the structure of nuclear star clusters, bulges, and star-forming knots are non-uniform. We generalize to cases with spherically-symmetric energy/mass injection that scale as $r^{-\Delta}$ within the starburst volume $R$, providing solutions for $\Delta = 0$, 1/2, 1, 3/2, and 2. In marked contrast with the CC85 model ($\Delta=0$), which predicts zero velocity at the center, for a singular isothermal sphere profile ($\Delta=2$), we find that the flow maintains a $\textit{constant}$ Mach number of $\mathcal{M}=\sqrt{3/5} \simeq 0.77$ throughout the volume. The fast interior flow can be written as $v_{r < R} = (\dot{E}_T/3\dot{M}_T)^{1/2} \simeq 0.41 \, v_\infty$, where $v_\infty$ is the asymptotic velocity, and $\dot{E}_T$ and $\dot{M}_T$ are the total energy and mass injection rates. For $v_\infty \simeq 2000 \, \mathrm{km \, s^{-1}}$, $v_{r<R} \simeq 820 \, \mathrm{km\, s^{-1}}$ throughout the wind-driving region. The temperature and density profiles of the non-uniform models may be important for interpreting spatially-resolved maps of starburst nuclei. We compute velocity resolved spectra to contrast the $\Delta=0$ (CC85) and $\Delta=2$ models. Next generation X-ray space telescopes such as XRISM may assess these kinematic predictions.