3 Main scientific drivers

The main scientific drivers of this new high sensitivity survey are the study of:

• The filamentary structures of the ISM, which under a variety of names such as shells, supershells, bubbles, worms, and so forth, are known to exist. The sizes and motions of these structures reveal aspects deeply rooted to the macroscopic energetics of the ISM. In particular, two systems which are outstanding for their very large extensions in the southern sky, are the shells surrounding the Sco-Cen association and the region of the Gum nebula;
• The Magellanic System, including in this definition the Magellanic Clouds, the intercloud gas, and the Magellanic Stream;
• The distribution and morphology of the so called High Velocity Clouds;
• New details of the galactic structure in classical items like the spiral arms, the warp, the rotation curve, the central region, and the Local Arm;
• The characteristics of the neutral phases of the ISM like relative abundances, z-extension, and filling factors;
• The gaseous counterpart of the infrared interstellar cirrus;
• The regions of exceptionally low total H I column density;
• The gas-to-dust relation.

Figure 3: H I profiles from the IAR survey at l = 293 $.\!\!^\circ$5; b = 10 $.\!\!^\circ$0: a) original data; and b) convolved to a velocity resolution of 8  $\rm\, km\, s^{-1}$

The results of the IAR H I Southern Sky Survey have been used to produce Figure 1, in which the integrated neutral hydrogen profiles, over the entire observed velocity range, are shown, on an Aitoff projection. The integrated intensities are represented by a gray scale, where the lowest intensities are represented by black, and the largest one, approximately 12000 K kms^-1, are depicted by white. In this figure are clearly seen both the galactic plane between l = 240$^\circ$ and l = 20$^\circ$ (with the galactic center in between), showing the various extensions at both sides of it, and the Magellanic System.

Global properties of the whole sky H I distribution can be appreciated in Fig. 2, which shows the same kind of display as Fig. 1, but with the addition of the Northern sky data as obtained by Hartmann & Burton ([1997]). This is the first time that such a display, with uniform data, is shown.

As mentioned above, the present survey will also be useful to build a new database of High Velocity Clouds (HVC), achieving a much better sensitivity, spatial resolution, and spatial coverage than in previous HVC surveys previously conducted (Morras et al. [1999]). This new H I survey will also allow to study in much more detail some of the HVC complexes known to date. Figures 3a and b are examples of the high quality of the IAR survey. Figure 3a shows the original data, while Fig. 3b shows the same data but convolved to a velocity resolution of 8 km s^-1.

Acknowledgements

This survey has been made possible, from the instrumental point of view, by the availability of a cooled receiver and a digital autocorrelator. The financial support obtained through a bilateral agreement between the Consejo Nacional de Investigaciones Científicas y Técnicas of Argentina (CONICET) and the Karlsruhe Forschungszentrum of Germany was crucial for developing the new front-end as well as the cooperation and support provided by the the Max-Planck-Institut für Radioastronomie through its Director, Dr. R. Wielebinski, and the electronic staff, headed by Eng. W. Zins and A. Schmidt, their help made it possible for Eng. J. Groismann (from the IAR) to build the receiver. For the digital backend we are also grateful to the Cornell University and the staff of the Arecibo Observatory for the equipments and the advices. Two of us (E.M.A. and J.J.L.) wish to thank the staff of the NAIC, with special mention of J. Hagen, M. Davies, R. Giovanelli and D. Campbell, for their warm hospitality and all the attention received during our stay at the Observatory. We would also like to thank the whole technical staff of the IAR for their constant attention to the radiotelescope. This work was partially supported by the CONICET under project PIP-4253/96.