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arXiv · 2504.21212

Dust in the Smith Cloud? A UV Investigation into the Smith Cloud's Gas-Phase Abundance Patterns

Johanna Vazquez·Kathleen Barger·Frances Cashman·Andrew Fox·Bart Wakker·Felix Lockman·Alex Hill·Suraj Poudel·April Horton·Jaq Hernandez·Matthew Nuss·Alice Blake·Lauren Corlies·Molly Peeples
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Abstract

The Smith Cloud is a high-velocity cloud (HVC) on its final approach to the Milky Way that shows evidence of interaction with the Galaxy's disk. We investigate the metallicity and gas-phase chemical depletion patterns in this HVC using UV absorption-line observations toward two background QSOs taken with the Hubble Space Telescope (HST)/Cosmic Origin Spectrograph (COS) and H I 21-cm emission-line observations taken with Green Bank Telescope (GBT). We find evidence of silicon gas-phase depletion with [Si/S]$=\,-0.72^{+0.26}_{-0.24}$ and [Si/O]$_{3\sigma}\,\lesssim\,-0.05$, implying the presence of dust within the Smith Cloud. Because dust is galactic in origin, this HVC could trace the return leg of a Galactic fountain or a dwarf galaxy that passed through the Galactic plane.

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Johanna Vazquez, Kathleen Barger, Frances Cashman, Andrew Fox, Bart Wakker, Felix Lockman, Alex Hill, Suraj Poudel, April Horton, Jaq Hernandez, Matthew Nuss, Alice Blake, Lauren Corlies, Molly Peeples. 2025-04-29. Dust in the Smith Cloud? A UV Investigation into the Smith Cloud's Gas-Phase Abundance Patterns. https://arxiv.org/abs/2504.21212

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