Small-Scale HI Channel Map Structure is Cold: Evidence from Na I Absorption at High Galactic Latitudes
Abstract
The spatial distribution of neutral hydrogen (H I) emission is a powerful probe of interstellar medium physics. The small-scale structure in H I channel maps is often assumed to probe the velocity field rather than real density structures. In this work we directly test this assumption, using high-resolution GALFA-H I observations and 50,985 quasar spectra from SDSS. We measure the equivalent widths of interstellar Na I D and Na I D absorption, and robustly conclude that they depend more strongly on the column density of small-scale structure in H I than on either the large-scale H I structure or the total H I column. This is inconsistent with the hypothesis that small-scale channel map structure is driven by velocity crowding. Instead, the data favor the interpretation that this emission structure predominantly originates in cold, dense interstellar material, consistent with a clumpy cold neutral medium.
Keywords
Cite
@article{arxiv.1909.09647,
title = {Small-Scale HI Channel Map Structure is Cold: Evidence from Na I Absorption at High Galactic Latitudes},
author = {J. E. G. Peek and S. E. Clark},
journal= {arXiv preprint arXiv:1909.09647},
year = {2020}
}
Comments
Submitted to the ApJL