A Spitzer-MIPS search for dust in compact high-velocity HI clouds

Abstract

We employ three-band Spitzer-MIPS observations to search for cold dust emission in three neutral hydrogen compact high-velocity clouds (CHVCs) in the vicinity of the Milky Way. Far-infrared emission correlated with HI column density was previously reported in HVC Complex C, indicating that this object contains dust heated by the Galactic radiation field at its distance of ~10kpc. Assuming published Spitzer, IRAS, and Planck IR-HI correlations for Complex C, our Spitzer observations are of sufficient depth to directly detect 160um dust emission in the CHVCs if it is present at the same level as in Complex C, but no emission is detected in any of the targets. For one of the targets (CHVC289) which has well-localized HI clumps, we therefore conclude that it is fundamentally different from Complex C, with either a lower dust-to-gas ratio or a greater distance from the Galactic disk (and consequently cooler dust temperature). Firm conclusions cannot be drawn for the other two Spitzer-observed CHVCs since their small-scale HI structures are not sufficiently well known; nonetheless, no extended dust emission is apparent despite their relatively high HI column densities. The lack of dust emission in CHVC289 suggests that at least some compact high-velocity clouds objects may exhibit very low dust-to-gas ratios and/or greater Galactocentric distances than large HVC complexes.

8 pages, 4 figures, text and Figure 4 substantially revised to include Planck results after referee report

References in corpus (14)

• A common mass scale for satellite galaxies of the Milky Way
• Distances to Galactic high-velocity clouds. I. Cohen Stream, complex GCP, cloud g1
• Seeding the formation of cold gaseous clouds in Milky Way size halos
• Distances to Galactic high-velocity clouds. Complex C
• An Accurate Distance to High-Velocity Cloud Complex C
• Where are the ``Missing'' Galactic Baryons?
• Smith's Cloud: A High-velocity Cloud Colliding with the Milky Way
• Metallicity and Ionization in High Velocity Cloud Complex C
• Head-Tail Clouds: Drops to Probe the Diffuse Galactic Halo
• Chandra and Far Ultraviolet Spectroscopic Explorer Observations of z~0 Warm-Hot Gas Toward PKS 2155-304
• Potential Condensed Fuel for the Milky Way
• X-Ray Searches for Emission from the WHIM in the Galactic Halo and the Intergalactic Medium
• Searching for Stars in Compact High-Velocity Clouds. II
• Molecular gas in high-velocity clouds: revisited scenario

Cited by in corpus (6)

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• All-sky census of Galactic high-latitude molecular intermediate-velocity clouds
• Physical effects on compact high-velocity clouds in the circumgalactic medium
• Detection of Dust in High-Velocity Cloud Complex C -- Enriched Gas Accreting onto the Milky Way