Survival and synthetic observables of neutral atomic hydrogen in galactic wind simulations

TL;DR

This paper uses numerical simulations to connect the physics of galactic winds with observable neutral hydrogen features, highlighting the roles of magnetic fields and recondensation in shaping HI gas properties.

Contribution

It introduces new synthetic HI observables from galactic wind simulations, emphasizing magnetic field effects and recondensation processes on HI morphology and spectra.

Findings

Magnetic fields influence HI morphology and spectral signatures.

Recondensation processes produce significant HI fractions in winds.

Magnetic orientation affects spectral line widths.

Abstract

Connecting numerical simulations to observations is essential to understanding the physics of galactic winds. Our Galaxy hosts a large-scale, multi-phase nuclear wind, whose dense gas has been detected using HI and molecular line observations. In this paper, we summarise our recent numerical work devoted to producing synthetic HI observables and measuring the properties of HI gas in galactic wind simulations. We discuss the evolution of radiative cloud systems embedded in star formation-driven galactic winds. Our shock-multicloud models show that multicloud gas streams are able to produce significant fractions of HI gas via recondensation. Our wind-cloud models show that magnetic fields have significant effects on the morphology and spectral signatures of HI gas. Cooling-driven recondensation, hydrodynamic shielding, and magnetic draping promote the survival of dense gas and the development of filamentary outflows. The orientation of magnetic fields also has an effect on synthetic observables, particularly on HI spectral lines. Transverse magnetic fields produce broader spectral lines of HI than aligned magnetic fields. Our models and analysis suggest that the fast-moving HI gas observed in the nuclear wind of our Galaxy may arise from multi-phase flows via recondensation.