Extragalactic large-scale structures behind the southern Milky Way - III. Redshifts obtained at the SAAO in the Great Attractor region

In the third of a series of papers on large-scale structures behind the sou thern Milky Way, we report here on redshifts obtained at the South African Astronomical Observatory (SAAO) in the Great Attractor region (318 deg less than or similar to l less than or similar to 340 deg, \b\ less than or equ al to 10 deg, Woudt 1998). This region encompasses the peak in the reconstructed mass density field, a ssociated with the Great Attractor (Kolatt et al. 1995, Dekel et al. 1998) and covers the crossing of the Super-galactic Plane with the Galactic Plane . Our deep optical galaxy search in the Zone of Avoidance (ZOA) in this regio n (Woudt 1998) has resulted in the detection of 4423 galaxies with observed diameters larger than 0.2 arcmin. We have obtained reliable redshifts for 309 galaxies of the 4423 galaxies with the "Unit" spectrograph (first with a Reticon, then with a CCD detector) at the 1.9-m telescope of the SAAO. An additional 13 tentative redshifts are presented. Before our survey, 127 ga laxies had a previously recorded redshift (NED and SRC96). Given a small ov erlap with the literature (44 galaxies), we present here redshifts for 265 galaxies that had no previous recorded-velocity in addition, we present cen tral velocity dispersion (sigma(o)) measurements for 34 galaxies in ACO 362 7. It is known that the Great Attractor (GA) region is overdense in galaxies a t a redshift-distance of v similar to 5000 km s(-1) (Fairall 1988, Dressler 1991, Visvanathan & Yamada 1996, di Nella et al. 1997). We realise here, h owever, that the Great Attractor region is dominated by ACO 3627 (hereafter referred to as the Norma cluster), a highly obscured, nearby and massive c luster of galaxies close to the plane of the Milky Way (l, b, v) = (325.3de g, -7.2deg, 4844 km s(-1)) (Kraan-Korteweg et al. 1996, Woudt 1998). Previous redshift surveys in the GA region have failed to gauge the signifi cance of the Norms cluster, primarily due to the diminishing effects of the Galactic foreground extinction on the partially obscured galaxies. In the absence of the obscuring effects of the Milky Way, the Norma cluster would have appeared as prominent as the well-known Coma cluster, but nearer in re dshift-space. This cluster most likely marks the bottom of the potential we ll of the Great Attractor (Woudt 1998).