Apparent total I magnitude: it

"it" is the apparent total I magnitude reduced to the Mathewson et al (1992) system.

The reduction of a given magnitude m to it is given by:

            it = m + a

where a is constant and given in the table below for each reference taken into account. The mean it magnitude is calculated as a weighted mean where the weight ("w", third column) is derived from each source of magnitude as the inverse square of the mean standard deviation. The final actual uncertainty sit is derived from the total weight.

The DENIS data are extracted from the provisional catalogue of 43,000 galaxies by Vauglin et al (1999) and Paturel et al (2003).

The DENIS I-band images were flat-fielded and de-biased at the Paris Data Analysis Center (PDAC) following the general procedure of treatment of DENIS data (Borsenberger 1997). Then, a special program was applied in order to bin images 2" x 2" and to replace the uniformized sky background by a constant value. The compressed images were then automatically transferred to Lyon to be processed. The source extraction was made with a very conservative threshold (2-sigma above the sky background). The galaxy extraction was made with a Discriminant Analysis based on seven parameters (peak intensity over area, Mean surface brightness, Peak intensity, Axis ratio, Relative surface object/matrix, Elongation of the matrix and Diffraction cross) and calibrated with a sample of 1146 DENIS objects visually classified as "galaxy", "star" or "unknown". A visual inspection of every galaxy candidate was made on the matrix of pixels.