The Southern Galactic Plane Survey: H I Observations and Analysis

We describe the H I component of the Southern Galactic Plane Survey (SGPS). The SGPS is a large-scale project to image at arcminute resolution the H I spectral line and 21 cm continuum emission in parts of the plane of the Milky Way. The survey covers Galactic longitudes 253^deg<=l<=358^deg and latitudes |b|<=1.5d (SGPS I), plus a first quadrant extension covering 5^deg<=l<=20^deg and |b|<=1.5d (SGPS II). The survey combines data from the Australia Telescope Compact Array and the Parkes Radio Telescope for sensitivity to angular scales ranging from 2' to several degrees. The combined data cover 325 deg² and have an rms sensitivity of 1.6 K. Here we describe the H I observations and data reduction in detail and present examples from the final data products. The complete data set is publicly available through the Australia Telescope National Facility's H I Surveys archive. This data set provides an unprecedented view of the neutral component of interstellar hydrogen in the inner Milky Way.