INTERGALACTIC STARS IN THE FORNAX CLUSTER

We have identified 10 candidate intergalactic planetary nebulae in the Fornax galaxy cluster. These objects were found during observations i n 1992 and 1993 in three fields chosen well away from any Fornax galax y at 15, 30 and 45 arcmin from the centre of Fornax. We used the usual method of blinking images taken in a narrow [O III] lambda 5007-Angst rom filter with images taken in an adjacent broad filter. The measured fluxes in the narrow, broad and I bands are consistent with these unr esolved objects being planetary nebulae immersed in an intergalactic p opulation of stars. Such a population is expected to arise as a conseq uence of tidal encounters between galaxies, and our findings strengthe n the case for the existence of such tidal debris. The confirmation of some or all of these 10 candidates as planetary nebulae would imply t hat intergalactic stars constitute a substantial fraction of all the s tars in Fornax, up to an estimated similar to 40 per cent. Intergalact ic planetary nebulae could prove useful in probing the underlying clus ter potential, since they would be far more abundant than galaxies. We discuss possible contamination of the sample by emission-line galaxie s, but conclude that planetary nebulae comprise the most likely identi fication for the detected objects.