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Astron. Astrophys. 352, 39-48 (1999)

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Extragalactic large-scale structures behind the southern Milky Way

III. Redshifts obtained at the SAAO in the Great Attractor region *

P.A. Woudt 1, R.C. Kraan-Korteweg 2 and A.P. Fairall 3

1 European Southern Observatory, Karl-Schwarzschild-Strasse 2, 85748 Garching, Germany
2 Departemento de Astronom[FORMULA]a, Universidad de Guanajuato, Apartado Postal 144, Guanajuato, Gto 36000, Mexico
3 Department of Astronomy, University of Cape Town, Rondebosch 7700, South Africa

Received 5 March 1999 / Accepted 8 October 1999


In the third of a series of papers on large-scale structures behind the southern Milky Way, we report here on redshifts obtained at the South African Astronomical Observatory (SAAO) in the Great Attractor region ([FORMULA], Woudt 1998).

This region encompasses the peak in the reconstructed mass density field, associated with the Great Attractor (Kolatt et al. 1995, Dekel et al. 1998) and covers the crossing of the Supergalactic Plane with the Galactic Plane.

Our deep optical galaxy search in the Zone of Avoidance (ZOA) in this region (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 galaxies had a previously recorded redshift (NED and SRC96). Given a small overlap with the literature (44 galaxies), we present here redshifts for 265 galaxies that had no previous recorded velocity. In addition, we present central velocity dispersion ([FORMULA]) measurements for 34 galaxies in ACO 3627.

It is known that the Great Attractor (GA) region is overdense in galaxies at a redshift-distance of [FORMULA] km s-1 (Fairall 1988, Dressler 1991, Visvanathan & Yamada 1996, di Nella et al. 1997). We realise here, however, that the Great Attractor region is dominated by ACO 3627 (hereafter referred to as the Norma cluster), a highly obscured, nearby and massive cluster of galaxies close to the plane of the Milky Way ([FORMULA], b, v) = (325.3[FORMULA], -7.2[FORMULA], 4844 km s-1) (Kraan-Korteweg et al. 1996, Woudt 1998).

Previous redshift surveys in the GA region have failed to gauge the significance of the Norma 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 redshift-space. This cluster most likely marks the bottom of the potential well of the Great Attractor (Woudt 1998).

Key words: catalogs – surveys – ISM: dust, extinction – galaxies: distances and redshifts – galaxies: clusters: individual: ACO 3627 – cosmology: large-scale structure of Universe

* All the tables are only available in electronic form at the CDS via anonymous ftp to ftp://cdsarc.u-strasbg.fr/pub/cats/J/A+A/352/39 ( or via http://cdsweb.u-strasbg.fr/cgi-bin/qcat?J/A+A/351/39

Send offprint requests to: P.A. Woudt (pwoudt@eso.org)

© European Southern Observatory (ESO) 1999

Online publication: November 23, 1999