Foreground: HI Column Density and Velocity

HI4PI High Velocity HI

Coordinate System:
Projection Type:
16.2 min
plate carrée, Hammer-Aitoff
Original Data Source:
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Westmeier (2018) used data from the HI4PI all-sky survey of HI 21-cm line emission to produce all-sky maps of the column density and velocity of high velocity clouds. High velocity 21-cm line emission was identified for each line of sight as emission for which the radial velocity deviates by more than 70 km s-1 from the velocity range that is allowed according to a simple model of Galactic rotation. The 5σ column density sensitivity is about 2.3 × 1018cm−2

HI column density maps and radial velocity maps in the LSR and GSR are available in both plate carrée and Hammer–Aitoff projections. The maps are provided as two-dimensional FITS images. Column density and GSR velocity maps in plate carrée projection are also available in Magellanic coordinates (using the definition of Nidever et al. 2008) in which the Magellanic Stream is aligned with the equator to facilitate studies of the Magellanic system. Note that for convenience the corresponding FITS files have Galactic coordinates defined in their header, as the FITS standard does not natively support the Magellanic coordinate system (Calabretta & Greisen 2002), while user-specific coordinate systems may not be supported by some of the third-party software commonly used to handle and display FITS images.

More details can be found in:

A new all-sky map of Galactic high-velocity clouds from the 21-cm HI4PI survey", Westmeier, T. (2018), MNRAS, 474, 289, ADS

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