Introduction

Understanding the origin of the peculiar velocity of the Local Group and the dipole in the Cosmic Microwave Background is one of the major goals of the study of large-scale structures. Theoretical reconstruction methods, however, still suffer from large interpolation uncertainties across the Zone of Avoidance (ZOA), which extends over about 25% of the optically visible extragalactic sky. Dynamically important structures might still lie hidden in this zone, such as the recently discovered nearby Dwingeloo galaxy (Kraan-Korteweg et al. 1994) and the rich massive cluster Abell 3627 (Kraan-Korteweg et al. 1996). Important large-scale structures, e.g., the Supergalactic Plane and other filaments and wall-like structures, seem to continue across this zone. Results from various theoretical approaches still vary strongly, however, in predicting clusters and voids even in the nearby universe (Sigad et al. 1998). This is mainly due to differences in the theoretical reconstruction methods and the adopted parameters, the different galaxy samples to which they are applied, and the selected interpolation mechanisms to bridge the scarcity of data in the ZOA. A more complete knowledge of the distribution of galaxies in redshift space as well as in distance space will improve the reconstructed galaxy density fields and reduce the diversity in the theoretical predictions.

Various approaches are presently being employed to uncover the galaxy distribution in the ZOA (cf.Kraan-Korteweg & Woudt, this volume): deep optical searches, NIR surveys (DENIS and 2MASS), far-infrared (FIR) surveys (e.g., IRAS), and blind HI searches. All methods produce new results, but all suffer from limitations and selection effects.  The combination of data from an optical galaxy search, a NIR survey and a systematic blind HI survey will allow us to examine the large-scale structures behind the southern Milky Way and the peculiar velocity field associated with them. Redshift independent distance estimates can be obtained via the NIR Tully-Fisher relation.

A deep optical survey in the southern ZOA is being conducted by one of us (Kraan-Korteweg & Woudt 1994, Kraan-Korteweg et al. 1995, 1996, and references therein). In this region (

,

), over 11000 previously unknown galaxies above a diameter limit of

and with

have been identified, next to the previously known Lauberts galaxies with

(Lauberts 1982). Galaxies can be identified visually for

(or typically down to about

depending on surface brightness and Galactic longitude).

The Multibeam (MB) survey of the ZOA, a systematic blind HI survey (Staveley-Smith 1997), will penetrate even the deepest extinction layers and trace gas-rich spirals out to redshifts of 12000km . The survey is currently being conducted with the Multibeam Receiver (13 beams in the focal plane array) at the 64m Parkes telescope and will cover the whole southern ZOA (

;

) with a detection limit of 10mJy.  Hardly any of the 1500 predicted detections are expected to have an optical counterpart, but at these latitudes many might be visible in the NIR. This new prospect becomes feasible with the currently ongoing NIR surveys such as DENIS (DEep NIR southern sky Survey; Epchtein 1997, Epchtein et al. 1997) and 2MASS (Skrutskie et al. 1997). First results from the DENIS survey, which is expected to cover the entire southern sky by the year 2001, are discussed in the following sections.

© Copyright Astronomical Society of Australia 1997