Ionization of Infalling Gas

TL;DR

This paper investigates the ionization state of infalling high-velocity gas clouds in the Galactic halo using H-alpha emission measurements, revealing how radiation and hydrodynamics influence their survival and interaction.

Contribution

It presents new H-alpha mapping results of Complex A and the Anti-Center Complex, enhancing understanding of halo gas ionization and dynamics.

Findings

H-alpha emission correlates with 21-cm emission in Complex A.

Faint H-alpha intensities (<100 mR) are detected in the halo clouds.

Ionized gas shows signs of interaction with the Galactic halo.

Abstract

H-alpha emission from neutral halo clouds probes the radiation and hydrodynamic conditions in the halo. Armed with such measurements, we can explore how radiation escapes from the Galactic plane and how infalling gas can survive a trip through the halo. The Wisconsin H-Alpha Mapper (WHAM) is one of the most sensitive instruments for detecting and mapping optical emission from the ISM. Here, we present recent results exploring the ionization of two infallling high-velocity complexes. First, we report on our progress mapping H-alpha emission covering the full extent of Complex A. Intensities are faint (<100 mR; EM <0.2 pc cm^-6 but correlate on the sky and in velocity with 21-cm emission. Second, we explore the ionized component of some Anti-Center Complex clouds studied by Peek et al. (2007) that show dynamic shaping from interaction with the Galactic halo.