3 Reductions

 The images were flatfielded using combined twilight and dome flats. The photometry was done with the MIDAS package developed by ESO. The images were combined, bias-subtracted and flatfielded using standard procedures. The subsequent reductions were done within the SURFPHOT context in MIDAS. The background was determined by fitting a tilted plane with FIT/BACKGROUND and was checked for correctness by measuring the sky level in different locations in the field. For each galaxy the centre and the ellipse parameters (ellipticity, position angle counted counter-clockwise from the horizontal axis) were determined at the level of $\sim25^{\mathrm{th}}\,\mathrm{mag}/\ifmmode\hbox{\rlap{$\sqcap$}$\sqcup$}\else{... ...$} \parfillskip=0pt\finalhyphendemerits=0\endgraf}\fi{\hbox{$^{\prime\prime}$}}$ by the ellipse fitting routine FIT/ELL3 and are given in Table 2.

  

Table 2: Parameters of the ellipse fits at approximatively $25 \,\mathrm{mag}/\ifmmode\hbox{\rlap{$\sqcap$}$\sqcup$}\else{\unskip\nobreak\h... ...$} \parfillskip=0pt\finalhyphendemerits=0\endgraf}\fi{\hbox{$^{\prime\prime}$}}$

These parameters were then used to obtain the total light profile (growth curve) by integrating the galaxy light in elliptical apertures of increasing equivalent radius. A surface brightness profile is obtained by differentiating the growth curve. The galaxy profiles derived in this way include the bright regions that usual ellipse fitting routines ignore. Circular aperture growth curves were also obtained as in Paper I. The resulting profiles by the elliptical aperture photometry are shown in Fig. 3 and the derived photometric parameters are shown in Table 1. The circular aperture photometry served as a comparison between the photometry presented here and that of Paper I. This comparison is given in Appendix A, where it is shown that the agreement between the two methods is excellent.

The profiles are traced down to the level where the errors due to the fluctuations in the sky level on the profile become dominant. As discussed in Sect. 4.4, this represents approx. $28.5\,\mathrm{mag}/ \ifmmode\hbox{\rlap{$\sqcap$}$\sqcup$}\else{\unskip\nobreak... ...$} \parfillskip=0pt\finalhyphendemerits=0\endgraf}\fi{\hbox{$^{\prime\prime}$}}$ in B and $27.5\,\mathrm{mag}/ \ifmmode\hbox{\rlap{$\sqcap$}$\sqcup$}\else{\unskip\nobreak... ...$} \parfillskip=0pt\finalhyphendemerits=0\endgraf}\fi{\hbox{$^{\prime\prime}$}}$ in R.

The photometric calibrations were done using standard methods, with calibration fields chosen to be relatively close on the sky to the observed galaxies. These fields were taken from Smith et al. (1985). The calibration stars were imaged before and after imaging every second galaxy.

Galactic absorption values were taken from the NED database, and are essentially zero for all galaxies in the sample (A_B = 0.00 for all galaxies except NGC5204 which has A_B=0.01). Therefore no correction was applied. A correction for internal extinction was not applied either.