Foreground

This is a composite all-sky map of neutral hydrogen column density (N_HI), formed from the Leiden/Dwingeloo survey data (Hartmann & Burton 1997) and the composite N_HI 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 N_HI 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 N_HI 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:

" Atlas of Galactic Neutral Hydrogen",
Hartmann & Burton, 1997, Cambridge University Press

" Stray-radiation correction as applied to the Leiden/Dwingeloo survey of HI in the Galaxy",
Hartmann et al. 1996, A&AS 119, 115

" HI in the Galaxy",
Dickey & Lockman 1990 Ann. Rev. A&A, 28, 215

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