2 Search criteria and method

A total of 19 POSSII R film copies, each comprising a field size of about 40 square degrees, were scanned. The longitude range selected was and in this interval all fields with centers at were examined. Table 1 displays the list of fields.

The main reasons for selecting this longitude range were:

1.

The Supergalactic Plane crosses the Galactic Plane at $\ell \sim 135\hbox{$^\circ$}$. The significance to probe the ZOA in a wide strip around this longitude is obvious - and is indicated by the fact that several bright galaxies (e.g. Maffei1 and 2, IC 342) lie behind the galactic plane.

2.

Beginning with $\ell \sim 160\hbox{$^\circ$}$, the surface density of galaxies in the ZOA sharply increases (Weinberger 1980) and the handling of data is thus made considerably more difficult; fortunately, a large set of data in the anticenter ZOA based on inspection of POSSI red-sensitive plates already exists (Pantoja 1995; Seeberger et al. 1996; Saurer et al. 1997).

  

Table 1: The fields of POSSII searched for our program

In an earlier paper (Seeberger et al. 1996) we have argued that red-sensitive surveys are the most suitable material for galaxy searches in the ZOA - hence our selection of the POSSII R films. The visual examination was done by one of us (MG) and a check of all objects together with the decision to finally accept or reject an object was done by RW. Individual films were scanned along overlapping strips of about 1 cm wide by use of a microscope at 16$\times$ magnification. Typically a film copy took about ten to twelve hours to scan.

Equatorial coordinates were determined using a high-resolution digitizer and a suitable software developed at Innsbruck. The overall accuracy is about $\pm 0\hbox{$.\mkern-4mu^\prime$}25$. Diameters of each galaxy candidate were determined using the microscope at 25$\times$ magnification and a glass plate with a 0.1mm grating; e.g., the major-axis diameter is defined as the maximum extent of the galaxy as seen by the eye through the microscope and is specified in increments of 0$\hbox{$.\mkern-4mu^\prime$}01$ (however, the diameters are not this accurate - about $\pm 0\hbox{$.\mkern-4mu^\prime$}05$ is probably more appropriate).