Speaker
Description
The 21 cm Spectral Line Observations of Neutral Gas with the VLA (21-SPONGE) survey detected HI absorption with exceptional optical depth sensitivity ($\sigma < 10^{-3}$) and matching HI emission with high angular resolution ($\sim 4^\prime$) towards 47 extragalactic radio continuum sources to study the physical properties of neutral hydrogen in the Milky Way. 9 of the background sources have multiple components and offer a unique way of probing HI properties on spatial scales $< 10^4$ AU. Cold HI features on AU-spatial scales, known as the tiny scale atomic structure (TSAS), have been observed since 1976. The origin of TSAS remains mysterious, and observations suggest that shocks and supernova remnants are likely important for the formation and survival of TSAS. All 9 of the multiple-component sources from 21-SPONGE are seen to undergo HI optical depth variations of at least $3\sigma$, with spatial separations between $\sim 500$ and $10^5$ AU. We compare the observed optical depth variations with predictions for turbulent fluctuations, and consider implications that TSAS has for heating of the ISM.
| Wish list question? | 10. What do theoretical models predict about the origin and fate of HI in and around galaxies? |
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