Interacting Galactic Neutral Hydrogen Filaments and Associated High-Frequency Continuum Emission

TL;DR

This study decomposes galactic HI emission into Gaussian components, revealing their association with high-frequency continuum emission observed by WMAP, and re-examines the free-free emission model in light of new data.

Contribution

It identifies specific HI component families linked to continuum peaks and evaluates the free-free emission model with revised parameters, suggesting a closer look at electron distribution.

Findings

Eighteen HI component families identified based on velocity and line width.

Strong spatial correlation between HI features and WMAP ILC peaks.

Estimated distances of 30 to 100 parsecs for associated HI-ILC features.

Abstract

Galactic HI emission profiles in an area where several large-scale filaments at velocities ranging from -46 km/s to 0 km/s overlap were decomposed into Gaussian components. Eighteen families of components defined by similarities of center velocity and line width were identified and related to small-scale structure in the high-frequency continuum emission observed by the WMAP spacecraft, as evidenced in the Internal Linear Combination (ILC) map of Hinshaw et al. (2007). When the center velocities of the Gaussian families, which summarize the properties of all the HI along the lines-of-sight in a given area, are used to focus on HI channel maps the phenomenon of close associations between HI and ILC peaks reported in previous papers is dramatically highlighted. Of particular interest, each of two pairs of HI peaks straddles a continuum peak. The previously hypothesized model for producing the continuum radiation (Verschuur, 2010) involving free-free emission from electrons is re-examined in the light of the new data. By choosing reasonable values for the parameters required to evaluate the model, the distance for associated HI-ILC features is of order 30 to 100 pc. No associated H-alpha radiation is expected because the electrons involved exist throughout the Milky Way. The mechanism for clumping and separation of neutrals and electrons needs to be explored.