2019/09/20 by J. E. G. Peek, S. E. Clark · 23 citations
Physics and Astronomy · #Absorption (acoustics) #Absorption spectroscopy #Astronomy and Astrophysical Research #Astrophysics and Star Formation Studies #Emission spectrum #Galaxies: Formation, Evolution, Phenomena #Interstellar medium #Measure (data warehouse) #Quasar #Sky #Spectral line #Spectroscopy #astro-ph.GA
paper · pdf · doi:10.3847/2041-8213/ab53de
published in The Astrophysical Journal Letters 886(1), L13 (IOP Publishing) · Submitted to the ApJL
arxiv created 2019/09/20 · openalex created_date 2019/09/26 · openalex publication_date 2019/11/15 · arxiv updated 2020/01/08 · openalex updated_date 2026/08/06
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 the Sloan Digital Sky Survey. We measure the equivalent widths of interstellar Na i D 1 and Na i D 2 absorption, and robustly conclude that together they depend nearly four times as 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.