Modeling the Accretion of High-Velocity Clouds from a Rotating Halo

TL;DR

This study models high-velocity cloud kinematics using simple simulations, supporting their origin in intermediate-halo dynamics and estimating a significant mass accretion rate that sustains star formation.

Contribution

It introduces a simple test-particle simulation approach to reproduce observed HVC kinematics and estimates their role in Galactic gas accretion and evolution.

Findings

Models with low angular momentum match observed HVC velocities.

Estimated mass accretion rate is several solar masses per year.

HVC dynamics are governed by intermediate-halo processes.

Abstract

High-Velocity Clouds (HVCs) are a major fuel reservoir for star formation in the Galactic disk. Determining their origin and kinematics is thus crucial for understanding Galactic evolution. In this paper, we employ simple test-particle simulations to model HVC kinematics, generating line-of-sight velocity maps and probability density functions (PDFs) for comparison with observational results. We find that models assuming low angular momentum and an initial scale of tens of kiloparsecs (kpc) successfully reproduce the observed kinematic trends for both blue-shifted and red-shifted components. This consistency may support the dominance of intermediate-halo dynamics (tens of kpc scale) in regulating Galactic evolution, consistent with HVC formation via thermal instability in metal-polluted gas in the halo. Furthermore, by considering the entire bulk mass involved in the continuous accretion process -- including diffuse or ionized components that often escape direct observation -- our theoretical estimates yield a total mass accretion rate of several solar masses per year. This indicates that HVC accretion has the potential to supply a sufficient amount of gas to the Galactic disk to sustain ongoing star formation over several Gyr. Our findings suggest that the Galactic baryon cycle and disk evolution are governed by dynamics within the intermediate halo, providing key kinematic constraints for future magnetohydrodynamical simulations that resolve spatial structures of high velocity clouds.