GCN: a gaseous Galactic halo stream?

Abstract

We show that a string of HI clouds that form part of the high-velocity cloud complex known as GCN is a probable gaseous stream extending over more than 50 deg in the Galactic halo. The radial velocity gradient along the stream is used to deduce transverse velocities as a function of distance, enabling a family of orbits to be computed. We find that a direction of motion towards the Galactic disk coupled with a mid-stream distance of ~20 kpc provides a good match to the observed sky positions and radial velocities of the HI clouds comprising the stream. With an estimated mass of 10^5 Msun, its progenitor is likely to be a dwarf galaxy. However, no stellar counterpart has been found amongst the currently known Galactic dwarf spheroidal galaxies or stellar streams and the exact origin of the stream is therefore currently unknown.

6 pages, 4 figures, accepted for publication in MNRAS

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• The high-velocity cloud complex Galactic Center Negative as seen by EBHIS and GASS. I. Cloud catalog and global properties
• A High-Velocity Cloud Impact Forming a Supershell in the Milky Way
• A population of high-velocity absorption-line systems residing in the Local Group
• Three-Dimensional Orientation of Compact High Velocity Clouds
• Estimating the Fuel Supply Rate on the Galactic Disk from High Velocity Clouds (HVCs) Infall