2 Selection of the observed fields

2.1 Observed fields

We selected 11 fields in the Fornax cluster which comprise giant galaxies as well as control fields without any bright Fornax galaxy. A mosaic of 4 fields matches the central giant elliptical NGC 1399 (named F1, F2, F3, and F4 as shown in Fig. 1). Five other target galaxies are the giant ellipticals NGC 1374, NGC 1379, and NGC 1427, the S0 galaxy NGC 1387, and the irregular NGC 1427A. The 2 additional fields (named B1 and B2 in the following) are located 13$\hbox{$^\prime$}$ and 95$\hbox{$^\prime$}$ east of NGC 1399, respectively. Note that field B2 is not suitable for an estimation of the absolute galaxy background, since it still lies in a region where Fornax member galaxies contribute to the galaxy counts, as seen in the radial density profiles of Ferguson (1989). All fields, except B1 and the four NGC 1399 fields, can serve as relative backgrounds to identify a possible excess population near NGC 1399 with respect to the "normal'' Fornax field galaxies. In total, our fields cover an area of about 600 square arcmin (or 0.17 square degree). Figure 1 is an extraction of the Digital Sky Survey and shows the location of all our fields except B2.

In a second observing run, 2 additional outlying background fields $10\hbox{$^\circ$}$north (B3) and $15\hbox{$^\circ$}$ south of NGC 1399 have been observed (see Sect. 3.1).

  

Figure 1: Image taken from the Digital Sky Survey, showing the observed CCD fields in the Fornax cluster. Field B2 lies outside this image to the east

2.2 Nomenclature of catalog fields

In the following the acronym CGF (Catalog of Galaxies in Fornax) will be used for the nomenclature of galaxies in the observed fields followed by a sequence number of the field and the sequence number of the galaxy in this field ordered by decreasing magnitude. For example, CGF 5-12 is the 12th brightest galaxy in field 5. The sequence numbers of the fields are ordered with increasing distance to the center of the Fornax cluster. The cross references to the CCD fields as described above are (see also Fig. 1): CGF 1 = F1 (NGC 1399, SE field), CGF 2 = F2 (NGC 1399, NE field), CGF 3 = F3 (NGC 1399, SW field), CGF 4 = F4 (NGC 1399, NW field), CGF 5 = B1, CGF 6 = NGC 1387, CGF 7 = NGC 1427A, CGF 8 = NGC 1379, CGF 9 = NGC 1374, CGF 10 = NGC 1427, and CGF 11 = B2.