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

Abstract

The analytic galactic wind model derived by Chevalier and Clegg in 1985 (CC85) assumes $\text{uniform}$ 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 $\text{constant}$ Mach number of $\mathcal{M}=\sqrt{3/5}\simeq 0.77$ throughout the volume. The fast interior flow can be written as $v_{r<R}=({\dot{E}}_T/3{\dot{M}}_T{)}^{1/2}\simeq 0.41v_{\infty }$, where $v_{\infty }$ is the asymptotic velocity, and ${\dot{E}}_T$ and ${\dot{M}}_T$ are the total energy and mass injection rates. For $v_{\infty }\simeq 2000\mathrm{km}{\mathrm{s}}^{-1}$, $v_{r<R}\simeq 820\mathrm{km}{\mathrm{s}}^{-1}$ 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.

submitted (13 October 2022), accepted MNRAS Letters (08 November 2022)

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