Dust in the Smith Cloud? A UV Investigation into the Smith Cloud’s Gas-phase Abundance Patterns Article Swipe

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Physics Cloud computing Abundance (ecology) Astrophysics Astronomy Gas phase Thermodynamics Fishery Operating system Biology Computer science

Jo Vazquez , Kathleen A. Barger , Frances H. Cashman , Andrew J. Fox , Bart P. Wakker , Felix J. Lockman , Alex S. Hill , Suraj Poudel , A. Horton , J. Hernández , Matthew Nuss , Alexander J. Blake , Lauren Corlies , Molly S. Peeples ·

YOU? · · 2025 · Open Access · · DOI: https://doi.org/10.3847/1538-4357/add2ee · OA: W4412729670

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/Cosmic Origin Spectrograph and H i 21 cm emission-line observations taken with Green Bank Telescope. We find evidence of silicon gas-phase depletion with [Si/S] = <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mo>−</mml:mo> <mml:mn>0.7</mml:mn> <mml:msubsup> <mml:mrow> <mml:mn>2</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>−</mml:mo> <mml:mn>0.26</mml:mn> </mml:mrow> <mml:mrow> <mml:mo>+</mml:mo> <mml:mn>0.24</mml:mn> </mml:mrow> </mml:msubsup> </mml:math> and [Si/O] 3 σ ≲ −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.