The Effelsberg-Bonn HI Survey: Milky Way gas. First data release

TL;DR

The Effelsberg-Bonn HI Survey (EBHIS) provides high-quality, high-resolution 21-cm data of the Milky Way and Local Volume, replacing older surveys with improved sensitivity and resolution, and making data publicly available.

Contribution

This paper introduces the first data release of EBHIS, a new all-sky HI survey with enhanced sensitivity, resolution, and data quality, using advanced instrumentation and calibration techniques.

Findings

EBHIS outperforms LAB in sensitivity and resolution.

EBHIS data matches LAB's intensity scale, enabling direct comparison.

Publicly available data includes a detailed Milky Way HI column density map.

Abstract

The Effelsberg-Bonn HI Survey (EBHIS) is a new 21-cm survey performed with the 100-m telescope at Effelsberg. It covers the whole northern sky out to a redshift of z~0.07 and comprises HI line emission from the Milky Way and the Local Volume. We aim to substitute the northern-hemisphere part of the Leiden/Argentine/Bonn Milky Way HI survey (LAB) with this first EBHIS data release, which presents the HI gas in the Milky Way regime. The use of a seven-beam L-band array made it feasible to perform this all-sky survey with a 100-m class telescope in a reasonable amount of observing time. State-of-the-art fast-Fourier-transform spectrometers provide the necessary data read-out speed, dynamic range, and spectral resolution to apply software radio-frequency interference mitigation. EBHIS is corrected for stray radiation and employs frequency-dependent flux-density calibration and sophisticated baseline-removal techniques to ensure the highest possible data quality. Detailed analyses of the resulting data products show that EBHIS is not only outperforming LAB in terms of sensitivity and angular resolution, but also matches the intensity-scale of LAB extremely well, allowing EBHIS to be used as a drop-in replacement for LAB. Data products are made available to the public in a variety of forms. Most important, we provide a properly gridded Milky Way HI column density map in HEALPix representation. To maximize the usefulness of EBHIS data, we estimate uncertainties in the HI column density and brightness temperature distributions, accounting for systematic effects.