# HI4PI

The HI4PI survey is an all-sky HI survey, based on data from the Effelsberg-Bonn HI survey (EBHIS) and from the third revision of the Parkes Galactic All-Sky Survey (GASS). The procedure used to merge the EBHIS and GASS datasets is described in the HI4PI survey paper (HI4PI collaboration 2016, see below). The resulting composite HI4PI dataset has an angular resolution of 16.2', spectral resolution 1.49 km/s and RMS sensitivity of 43mK per channel.

CADE delivers a suite of image moments generated from the HI4PI data in Galactic and Equatorial (J2000) coordinates.

The HI column density map has units of `cm-2`. This map is obtained by multiplying the moment-0 map (see below) by a uniform prefactor. No opacity correction is applied.

The peak brightness map has units of `K`. This is the maximum intensity along the spectral axis for each line of sight.

The integrated intensity (moment-0) map has units of `K.km/s`. This is direct integration of the spectral cube along the velocity axis. No masking is applied.

The intensity-weighted mean radial velocity map (moment-1) has units of `km/s`. For sightlines with a single velocity component, the moment-1 reflects the average velocity of the emission. In the case of line profiles with two or more velocity components, the moment-1 will sit intermediate between the components.

The equivalent width map is a linewidth metric, and is calculated as the integrated intensity divided by the peak brightness. It has units of `km/s`. This is the rectangular width needed to supply the full line width at the peak intensity. A prefactor is then applied to recast as the equivalent sigma for the case of a Gaussian line profile. This is a highly robust statistic in the sense that it behaves well in the presence of noise or multiple components. It can easily miss subtleties in the line profile and has some dependence on spectral resolution. Not corrected for the line spread function (channel width + channel-to-channel correlation), nor for biases due to finite sensitivity.

#### Reference

'HI4PI: A full-sky H I survey based on EBHIS and GASS' by HI4PI Collaboration, 2016, A&A, 594, 116 http://adsabs.harvard.edu/abs/2016A%26A...594A.116H

#### HiPS

HI4PI NHI HiPS are available in Aladin Collections/Image