HI4PI: A full-sky HI survey based on EBHIS and GASS

TL;DR

The HI4PI survey provides a high-resolution, sensitive, and fully sampled all-sky map of Galactic neutral hydrogen, surpassing previous surveys like LAB in quality and coverage.

Contribution

This paper introduces the HI4PI survey, combining EBHIS and GASS data to create a superior all-sky HI dataset with improved resolution, sensitivity, and sampling.

Findings

Outperforms LAB in resolution and sensitivity

Provides full-sky, fully sampled HI maps

Enables better astrophysical analyses of Galactic HI

Abstract

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.