Surface brightness profiles of dwarf galaxies in the NGC 5044 Group: A critical revision of the luminosity - shape relation as a distance indicator

CELLONE, S. A.

ASTRONOMY AND ASTROPHYSICS

The European Southern Observatory - EDP Sciences

Año: 1999 vol. 345 p. 403 - 413

0004-6361

CCD surface photometry of a small sample of dwarf and intermediate luminosity elliptical galaxies in the NGC 5044 Group is presented. Their surface brightness profiles are fitted with a Sérsic law, and it is shown that a few relatively bright galaxies with “convex” profiles destroy the known relation between total magnitude and the “shape” parameter (N) of the model, thus ruling out the use of this relation as a distance indicator for individual galaxies. Even eliminating these deviant galaxies, as well as those with poor quality profiles, the scatter of the luminosity – shape relation remains relatively high, despite that depth effects should not be important in this small group of galaxies. In addition, the fact that there is a lower limit in the size of galaxies which can be resolved in more distant clusters causes the observed luminosity – shape relation to change both its slope and its zero point as distance increases, limiting alsoits practical use as a distance indicator for groups of galaxies.An alternative is explored using the known relation between integrated magnitude and effective surface brightness as a distanceindicator, and it is found that its zero point also changes depending on the mean sizes of the galaxies included in each sample. Mean distances for groups of galaxies obtained with this method should then be taken with care.The effects of seeing on the derived photometric parameters are also investigated in an empirical way.Three very faint, previously non-catalogued, dwarfspheroidal galaxies were also detected, and their photometric data are given, along with their coordinates.