# Small-scale structure traced by neutral hydrogen absorption in the direction of multiple-component radio continuum sources

27 Apr 2020 Rybarczyk Daniel R. Stanimirovic Snezana Zweibel Ellen G. Murray Claire E. Dickey John M. Babler Brian Heiles Carl

We have studied the small scale distribution of atomic hydrogen (HI) using 21-cm absorption spectra against multiple-component background radio continuum sources from the 21-SPONGE survey and the Millennium Arecibo Absorption Line Survey. We have found $>5\sigma$ optical depth variations at a level of $\sim0.03-0.5$ between 13 out of 14 adjacent sightlines separated by a few arcseconds to a few arcminutes, suggesting the presence of neutral structures on spatial scales from a few to thousands of AU (which we refer to as tiny scale atomic structure, TSAS)... (read more)

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