6 Summary

We have presented a new procedure for obtaining total-magnitude estimates from unsaturated galaxy images. This method involves first smoothing two-dimensional digital images numerically (ideally convolving them with a two-dimensional radially symmetric Gaussian function of sufficient FWHM), in order to produce lower-resolution images, which are then parameterised using elliptical isophotes. The rationale behind this is that even the faintest isophotes of the synthetic lower-resolution images (which cannot be measured accurately or at all in practice) become distorted in a predictable manner by the smoothing process. The second stage involves modeling the resulting surface-brightness profiles with Sérsic functions, and extrapolating the best-fitting functions to infinite radial distances. We have also demonstrated the system's high level of stability with respect to galaxy morphological type, limiting isophote as well as the size of the seeing disc (and thereby degree of smoothing too).

Acknowledgements

We would like to thank Jon Godwin for providing the photometry software and Steve Maddox for a useful discussion. This work made use of the computing facilities of the QSO & Observational Cosmology Group at BAO (which are funded by the Chinese Natural Science Foundation) and those of Starlink. CKY gratefully acknowledges a PDRF from the National Postdoctoral Fellowship Office of China.