Appendix: Elliptical vs. circular aperture photometry

We here compare the method used in this paper and that used in Paper I, i.e. elliptical vs. circular aperture photometry. Figures 6 to 10 compare the different photometric parameters obtained with the two methods. The comparison is useful for future studies of a sample of galaxies measured by either of these two methods.

  

Figure 6: Comparison between the total apparent magnitude $B_{\rm T}$obtained with elliptical and circular aperture photometry

From Fig. 6 one can see the excellent agreement between the elliptical and the circular aperture photometry as far as the total magnitudes are concerned. The vast majority of the galaxies show differences less than $0.025 \,\mathrm{mag}$.

  

Figure 7: Comparison between the effective radius obtained with elliptical and circular aperture photometry. The leftmost object corresponds to NGC 5229

Figure 7, shows that the effective radius measurements strongly depend on the apparent shape of the galaxies. Elongated galaxies, as illustrated by NGC 5229, which has an apparent ellipticity of $\epsilon=0.81$, show different effective radii as measured by the different methods. In such cases the circular aperture photometry is clearly inadequate.

  

Figure 8: Comparison between the effective surface brightness obtained with elliptical and circular aperture photometry. The leftmost object corresponds to NGC 5229

The effective surface brightness obtained by the two methods show reasonable agreement except, as noted above and for the same reasons, in the case of very elongated objects, see Fig. 8.

As can be seen in the plots for the exponential fit parameters $\mu_0$and $\alpha$, Figs. 9 and 10, the circular apertures yield slightly larger scale-lengths and lower central surface brightnesses on average than the elliptical apertures.

  

Figure 9: Comparison between the central extrapolated surface brightness obtained with elliptical and circular aperture photometry

  

Figure 10: Comparison between the exponential profile parameter $\alpha$obtained with elliptical and circular aperture photometry

Acknowledgements

T.B. and B.B. thank the Swiss National Science Foundation for financial support. We also thank Frank Thim for taking part in the observing run and the referee for useful comments.

This research has made use of the NASA/IPAC Extragalactic Database (NED) which is operated by the Jet Propulsion Laboratory, California Institute of Technology, under contract with the National Aeronautics and Space Administration, as well as NASA's Astrophysics Data System Abstract Service.