HI4PI: A full-sky HI survey based on EBHIS and GASS
  Measurement of the Galactic neutral atomic hydrogen (HI) column density, NHI,
and brightness temperatures, Tb, is of high scientific value for a broad range
of astrophysical disciplines. In the past two decades, one of the most-used
legacy HI datasets has been the Leiden/Argentine/Bonn Survey (LAB). We release
the HI 4$\pi$ survey (HI4PI), an all-sky database of Galactic HI, which
supersedes the LAB survey. The HI4PI survey is based on data from the recently
completed first coverage of the Effelsberg-Bonn HI Survey (EBHIS) and from the
third revision of the Galactic All-Sky Survey (GASS). EBHIS and GASS share
similar angular resolution and match well in sensitivity. Combined, they are
ideally suited to be a successor to LAB. The new HI4PI survey outperforms the
LAB in angular resolution (16.2', FWHM) and sensitivity (RMS: 43 mK). Moreover,
it has full spatial sampling and thus overcomes a major drawback of LAB, which
severely undersamples the sky. We publish all-sky column density maps of the
neutral atomic hydrogen in the Milky Way, along with full spectroscopic data,
in several map projections including HEALPix.
