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The Space Density of Primordial Gas Clouds near Galaxies and Groups and their Relation to Galactic HVCs

M. A. Zwaan·F. H. Briggs
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Abstract

The Arecibo HI Strip Survey probed the halos of ~300 cataloged galaxies and the environments of ~14 groups with sensitivity to neutral hydrogen masses > 10^7 M_sun. The survey detected no objects with properties resembling the High Velocity Clouds (HVCs) associated with the Milky Way or Local Group. If the HVCs were typically M_HI=10^{7.5} M_sun objects distributed throughout groups and galaxy halos at distances of 1 Mpc, the survey should have made ~70 HVC detections in groups and ~250 detections around galaxies. The null detection implies that HVCs are deployed at typical distances of <200 kpc from the galaxies or group barycenters. If the clouds are in virial equilibrium, their average dark matter fraction must be 98% or higher.

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M. A. Zwaan, F. H. Briggs. 2000-01-03. The Space Density of Primordial Gas Clouds near Galaxies and Groups and their Relation to Galactic HVCs. https://doi.org/10.1086/312488

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