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8th of December 2017
A new all-sky map of high-velocity clouds
by Tobias Westmeier (ICRAR/UWA)
Using the recent data release from the HI4PI survey, Westmeier (2018) created a new all-sky map of HI emission from high-velocity clouds (HVCs) with significantly better spatial resolution and sensitivity as compared to previously available data. The map was generated by masking out HI emission at velocities consistent with the regular rotation of the Galactic disc, leaving only the emission from HVCs and a few nearby galaxies.

In the false-colour map shown above, brightness corresponds to HI column density, while hue reflects the radial velocity of the emission. Apart from the two Magellanic Clouds, numerous HVC complexes and filaments are visible, including the large complex C in the northern hemisphere as well as the extended filaments of the Magellanic Stream and Leading Arm in the south. Overall, about 13% of the sky is filled with HVC gas above a column density threshold of 2 × 1018 cm−2, although we presumably only see the tip of the iceberg, as ionised gas and HI gas at radial velocities similar to those of the Galactic disc will be missing from the new map. FITS images of the HVC map have been made available to the entire community.

Reference: Westmeier, T., 2018, MNRAS, 474, 289 (DOI | ADS | arXiv)

Press release: Astronomer’s map reveals location of mysterious fast-moving gas (04/12/2017)

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