On modelling CC85 wind in an expanding local box

TL;DR

This paper derives hydrodynamic equations for a local, expanding wind model based on the Chevalier & Clegg (1985) framework, aiding the study of small-scale multiphase gas in galactic outflows.

Contribution

It provides the first explicit derivation of local hydrodynamic equations for an expanding wind in a local box, accounting for anisotropic expansion effects.

Findings

Derived hydrodynamic equations for local wind modeling.

Highlighted anisotropic source terms due to transverse expansion.

Facilitates realistic small-scale multiphase outflow simulations.

Abstract

The Chevalier & Clegg (1985) spherical wind is widely used to model galactic outflows. Efforts are underway to understand the production of multiphase gas in such outflows. Since the important scales for the multiphase gas are very small compared to the size of the wind, it is very useful to have a local model of the cold gas interacting with a volume-filling expanding wind. In this note we explicitly derive the governing hydrodynamic equations in such a local box for the first time. We highlight that the expansion in a wind occurs only in the transverse direction, and this results in anisotropic source terms in the momentum equation. Our equations will be very useful in realistic modelling of the small scale structure of multiphase galactic outflows. [original note does not include an abstract]