Intergalactic stars in the Fornax cluster

We have identified ten candidate intergalactic planetary nebulae in theFornax galaxy cluster. These objects were found during observations in 1992 and1993 in three fields chosen well away from any Fornax galaxy at 15 arcmin, 30arcmin, and 45 arcmin from the centre of Fornax. We used the usual method ofblinking images taken in a narrow OIII filter, with images taken in an adjacentbroad filter. The measured fluxes in the narrow, broad, and I bands areconsistent with these unresolved objects being planetary nebulae immersed in anintergalactic population of stars. Such a population is expected to arise as aconsequence of tidal encounters between galaxies, and our findings strengthenthe case for the existence of such tidal debris. The confirmation of some orall of these ten candidates as planetary nebulae would imply that intergalacticstars constitute a substantial fraction of all the stars in Fornax, up to anestimated 40 per cent. Intergalactic planetary nebulae could prove useful inprobing the underlying cluster potential, since they would be far more abundantthan galaxies. We discuss possible contamination of the sample by emission-linegalaxies, but conclude that planetary nebulae is the most likely identificationfor the detected objects. keywords: intergalactic medium-- galaxies:interactions -- planetary nebulae: general -- clusters: individual: FornaxComment: 5 pages, latex (mn.sty), 3 figures (figure 1 is a jpeg image), to be published by MNRA