The HI Southern Galactic Plane Survey

By Naomi McClure-Griffiths

Under the supervision of Dr. John M. Dickey

ABSTRACT

We present the Southern Galactic Plane Survey (SGPS), a survey of the neutral hydrogen (H I) in the inner Milky Way. The SGPS is a survey of the H I spectral line and 21 cm continuum emission in the fourth quadrant of the plane of the Galaxy. It covers 210 square degrees, spanning the region l = 2530-3580 and |b| <= 10 at an angular resolution of ~2 arcmin, a velocity resolution of 0.8 km s-1 and to a sensitivity limit of ~2 K. High resolution data were obtained with the Australia Telescope Compact Array (ATCA) and combined with data obtained with the Parkes Radio Telescope for complete coverage of structures ranging in angular size from 2 arcmin to 2 degrees. In addition, the low resolution Parkes survey was expanded to |b| <= 100 for sensitivity to extremely large-scale structures. The survey is part of a large scale effort to understand the structure, dynamics and thermal phases of the ISM throughout the Milky Way.

We use the SGPS dataset to study the properties of large scale emission structures in the ISM, specifically H I shells, supershells, and chimneys. H I shells are among the largest objects in the ISM with radii between tens of parsecs and kiloparsecs. As such, they are a major constituent in the Galactic energy budget and drive much of the dynamics of the ISM. H I shells, which are formed through the combined effects of stellar winds and supernovae, outlast the radiative lifetimes of their parent H II regions and supernova remnants and thereby provide lasting fossils of the effects of massive stars on the ISM. In order to explore these effects, we here present a new catalog of large H I shells in the Southern Milky Way. We discuss their individual and global properties as well as their distribution in an attempt to probe deeper into the feedback processes of stellar life and death and the circulation of matter between the Galactic disk and halo.