Foreground: HI Column Density
The data made available through this page have been superseded by the Effelsberg-Bonn HI survey and the GASS HI survey.
survey dependent:~0.5°- ~1°
HEALPix, nested, res 9 (Nside=512)
This is a composite all-sky map of neutral hydrogen column density (NHI), formed from the Leiden/Dwingeloo survey data (Hartmann & Burton 1997) and the composite NHI map of Dickey & Lockman (1990). The two datasets are not matched in sensitivity or resolution; note that discontinuities exist in the constructed composite map. A pixel mask is provided to indicate which dataset was used for each location on the sky.
Hartmann & Burton provide a velocity integrated (-450 km/s < V_lsr < +400 km/s) HI brightness temperature map in Galactic coordinates, sampled every 0.5 degrees. This entire data set was converted to NHI by multiplying by their factor of 1.8224e18 K km s-1 cm-2 and then interpolated to pixel centers appropriate for HEALPix Nside=512. Since the Leiden/Dwingeloo survey does not have sky coverage for declinations < -30°, the lower resolution Dickey & Lockman map was also interpolated to HEALPix and used to fill in the coverage gap. The Dickey & Lockman NHI map is itself a composite of several surveys which had been merged and averaged onto 1° bins in Galactic coordinates. Their map includes emission between -250 km/s < V_lsr < 250 km/s (excluding the LMC and SMC).
More details can be found in: