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Subsections

3 Results and discussion

3.1 The catalogue

In Table 2 we list our galaxy candidates in order of increasing galactic longitude. Due to the editorial policy of Astronomy and Astrophysics we publish this table, which comprises 58 print pages, in electronic form. Thus, only a sample page (the first page of Table 2) is given here.

The galaxy designations follow the IAU recommendation for the nomenclature of new objects: ZOAGG$\ell\ell\ell.\ell\ell\pm bb.bb$.ZOAG means "Zone of Avoidance Galaxy", G stands for galactic coordinates, and $\ell\ell\ell.\ell\ell$ and $\pm bb.bb$ are galactic longitude and latitude, respectively.

  
Table 2: The catalogue

\begin{tabular}
{lcccccl}
\hline
ZOAG G & $\alpha$(1950) & $\delta$(1950) & 
$\a...
 ...8 06.5 & 56 57 06 & 00 10 44.5 & 57 13 47 & 0.10 0.08 & \\  
\hline\end{tabular}

In Col. 1 the designation of the galaxies is given. For reasons of brevity the prefix ZOAGG is omitted. In a few cases, this designation is not unambiguous, i.e. 2 (or more) very closely located galaxies could not be separated. For this we add a suffix "a'' for the object with the smaller (smallest) right ascension. If the right ascensions are practically the same, then the object with the smallest declination is given the suffix "a'', then "b'' for the next higher declination and so forth. If both R.A. and Dec. are almost identical, then (and only then) the more optically extended one of the objects gets the suffix "a". Columns 2 and 3 give the equatorial coordinates for epoch 1950.0, Cols. 4 and 5 for epoch 2000.0 (Julian). In Col. 6 we present maximum and minimum diameters (in arcmin) measured from the POSSII R film copies. In the last column we list cross-identifications with galaxies taken from the NASA Extragalactic Database (NED), and with IRAS point sources taken from SIMBAD. For cross-identifications with the IRAS PSC catalogue we used our above-given positional uncertainty and checked whether our optical error bars fell within the IRAS uncertainty ellipse or not.

3.2 The distribution

In Fig. 1 (top) all our galaxy candidates are plotted, and in Fig. 1 (bottom) the 100 $\mu$m IRAS surface brightness is shown. From Fig. 1 (top), several distinctive features are obvious: First, the ZOA does not appear to be prominent (particularly if compared, e.g., with Fig. 3 in Seeberger et al. (1994) that is based on galaxy candidates found on POSSI) - there are numerous galaxy candidates even very close to the galactic equator. Second, the number of galaxies at negative galactic latitudes is much larger than at positive ones. Third, there are only very few objects at $\ell \mathrel{\mathchoice {\vcenter{\offinterlineskip\halign{\hfil
$\displaysty...
 ...ip\halign{\hfil$\scriptscriptstyle ... at positive latitudes. The distribution of galaxies can be influenced in two main ways, i.e. it can be of   i) galactic (i.e. foreground) origin and/or it can   ii) reflect the true distribution, like concentrations (clusters) of galaxies. The former

  
\begin{figure}
\begin{center}

\includegraphics [width=17.5cm]{ds1701f1a.ps}
 

\includegraphics [width=17.5cm]{ds1701f1b.ps}
\end{center}\end{figure} Figure 1: Top: Distribution of the galaxies in galactic coordinates. The south-west corners of the fields lack objects due to an area containing sensitometer spots. Bottom: A grayscale map of IRAS 100 $\mu$m intensities (white corresponds to bright emission). Regions outside the surveyed area are black
origin might, in part, be tested by comparing the galaxy distribution with maps of (infrared emitting) dust clouds. As can easily be seen from a comparison of Fig. 1 (top) with 1 (bottom), regions of intense IR-emission are generally avoided by galaxies; however, in a few cases there appear to be positional coincidences that must be examined, since e.g. small red nebulae in star forming regions sometimes mimic the appearance of obscured galaxies, since they cannot be easily eliminated even if checking plates taken in the photographic infrared (like POSS II IR).

3.3 Completeness of the catalogue

The limit of completeness of the catalogue may be estimated by plotting the number of galaxies with diameters larger or equal than a certain value against this value. For a homogeneous spatial distribution of galaxies having all the same typical linear dimension $N \sim d^{-3}$ applies. Figure 2 shows that our sample of galaxies starts to seriously deviate from completeness at angular diameters of $d \le$ 0$.\mkern-4mu^\prime$2. Similar optical surveys performed at the POSSI plates were almost complete for $d \ge$ 0$.\mkern-4mu^\prime$4 (Seeberger et al. 1996; Lercher et al. 1996). Certainly our better limit of completeness is due to the higher quality of the POSSII plates, especially thanks to a finer grain emulsion. The figure also indicates that we missed roughly 73% of galaxies with diameters less than 0$.\mkern-4mu^\prime$1. When comparing to Seeberger et al. (1996) who missed roughly 90% of this sized galaxies one can guess that $\approx$ 3 $\times$ more galaxy candidates will be selected on POSSII R plates than on POSSI E.

Nevertheless, we were able to directly compare the total number of galaxy candidates selected in optical surveys on POSSI E and POSSII R plates since a substantial portion of our region was already surveyed on the older plates (Lercher et al. 1996; Saurer et al. 1997). By counting the galaxies in the intersection of both surveys we obtained 674 and 2072 galaxies detected on POSSI and POSSII, respectively. Thus, we may roughly state that on the "new" POSS R plates (i.e. POSSII) 3.1 $\times$ more galaxy candidates are selected than on the "old" ones.

  
\begin{figure}
\begin{center}

\includegraphics [width=7cm]{ds1701f2.ps}
\end{center}\end{figure} Figure 2: Squares: logarithm of the total number of galaxies down to a given angular diameter versus the logarithm of this very diameter. The line corresponds to the expected slope of -3

3.4 IRAS two-colour diagram

Out of our sample of 3455 galaxies 144 have an IRAS counterpart (as results from the check of the NED and SIMBAD catalogue), i.e. 0.26 galaxies per square degree. This value is not larger than that found for POSSI surveys (Seeberger et al. 1996 and references therein). Similarly to Seeberger et al. (1996) we plotted a two-colour diagram of the IRAS point sources for those with a flux quality $\ge$ 2 (see Fig. 3). From our sample 43 sources fulfilled this condition, giving almost identical mean colours as quoted in Seeberger et al. (1996).

  
\begin{figure}
\begin{center}

\includegraphics [width=8cm]{ds1701f3.ps}
\end{center}\end{figure} Figure 3: IRAS two-colour diagram for 43 galaxies with fluxes of a good quality

Acknowledgements

This work was supported by the "Jubiläumsfonds der Österreichischen Nationalbank'' under project No. 5776. We would also like to thank S. Kimeswenger, W. Marchiotto and S. Temporin for various help.

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, Caltech, under contract with the National Aeronautics and Space Administration.

We have made use of the SIMBAD database which is managed by the Centre de Données astronomiques de Strasbourg (CDS).


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