A Deep Optical Galaxy Search in the Southern ZOA

To reduce the -wide strip of the ZOA, we have embarked on a deep search for partially obscured galaxies, i.e., down to fainter magnitudes and smaller dimensions compared to existing catalogues. To date, 50 fields of the ESO/SRC-survey have been visually inspected. The surveyed area lies within - its borders are outlined in Fig. 1. Within the surveyed area of , 10276 new galaxies with have been identified in addition to the 269 Lauberts galaxies with within this area (Lauberts 1982). Their distributions are displayed in Fig. 1.

 
Figure 1: The galaxy distribution from our deep galaxy search () and the Lauberts galaxies () in Galactic coordinates. The to date surveyed region is outlined. The dipole direction in the CMB, the center of the GA and the most prominent clusters are marked. The contours mark absorption in the blue of = (thick contour), as derived from the Galactic HI (Kerr et al. 1986), adopting a constant gas-to-dust ratio and the formalism given by Burstein & Heiles 1982.

Details on the search can be found in Kraan-Korteweg & Woudt 1994.

In the mean, the galaxy density is well correlated with the foreground extinction A as traced by the HI-column-density: for (thick contour), respectively , the ZOA remains opaque. Above this band, distinct filaments and round concentrations uncorrelated with the foreground dust can be recognized, thus they must have their origin in extragalactic large-scale structures. Some of these features seem to align with the known galaxy distribution, as e.g., a filament above the Galactic Plane which points toward the Centaurus cluster, and the filament from the Hydra and Antlia clusters towards the prominent overdensity in Vela. A significant overdensity, centered on the previously identified cluster A3627 (Abell et al. 1989), is evident within only a few degrees of the predicted center of the GA. It is the only Abell cluster behind the Milky Way, classified as rich and nearby and lies within the GA region. Even so, this cluster has received little attention because of the diminishing effects of the foreground obscuration. And this cluster at ) is hardly obvious in the distribution of Lauberts galaxies and not at all in IRAS samples. However, the galaxies in this overdensity are on average relatively large (just below the diameter limit of Lauberts). Lifting the obscuring veil of the Milky Way by correcting the observed properties of the galaxies for the foreground extinction would, in fact, reveal this cluster as the most prominent overdensity in the southern sky.

Redshift measurements are required to map the galaxies in 3 dimensions. The 2-dimensional galaxy distribution alone can be misleading. For instance, the prominent overdensity in Vela was found to be due to a superposition of a nearby ( km ) filament connecting to Hydra, a more distant (6000 km ) shallow extended supercluster, and a very distant ( km ) wall-like structure crossing the ZOA (Kraan-Korteweg et al. 1994).

© Copyright Astronomical Society of Australia 1997