Introduction

NGC 6744 is one of the largest, nearest ( Mpc), and most spectacular spiral galaxies in the southern sky, and yet it has received surprisingly little attention. In part, this can be attributed to its large angular size (the B=25 mag arcsec^-2 isophote spanning some

20' x 13') which, besides yielding a relatively low surface brightness disk, exceeds the field of view of most existing optical and radio imaging systems. The recent advent of large format optical CCD arrays, and a mosaic observing mode with the Australia Telescope Compact Array (ATCA) have at last made it feasible to carry out a full investigation of the stellar and gaseous components of NGC 6744. This paper outlines some preliminary results of our HI observations.

Our study of NGC 6744 was primarily motivated by a desire to understand the influence of the spiral density wave pattern on star formation. NGC 6744 is morphologically very similar to our Galaxy (de Vaucouleurs 1983), but is unusually isolated, with no nearby companion akin to M31. However, deep optical images suggest also some form of interaction between NGC 6744 and the small blue irregular galaxy NGC 6744A, and possibly with a host of other dwarf galaxies in the vicinity. In addition, NGC 6744 is listed in the Catalog of Southern Ringed Galaxies (Buta 1995) as having an inner ring

in diameter. As has been shown in our earlier ATCA HI study of the ringed barred spirals NGC 1433 and NGC 6300 (Ryder et al. 1996), associating such ring features with specific orbital resonances (in this case, the inner second harmonic resonance) is a powerful technique for measuring directly such fundamental dynamical parameters as the bar pattern speed.

© Copyright Astronomical Society of Australia 1997