The Local Group Census: planetary nebulae in the spheroidal galaxies NGC 147, NGC 185 and NGC 205^*

¹ Isaac Newton Group of Telescopes, Apartado de Correos 321, 38700 Santa Cruz de La Palma, Spain e-mail: rcorradi@ing.iac.es
² Dipartimento di Astronomia e Scienza dello Spazio, Universitá di Firenze, L.go E. Fermi 2, 50125 Firenze, Italy
³ Institute of Astronomy, University of Cambridge, Madingley Road, Cambridge CB3 0HA, UK
⁴ Instituto de Astrofísica de Canarias, c. vía Láctea s/n, 38200, La Laguna, Tenerife, Spain
⁵ APS Division, Dept. of Pure and Applied Physics, Queen's University Belfast, Belfast BT7 9NN, Northern Ireland, UK
⁶ ST-ECF, ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany
⁷ Physics Department, UMIST, PO Box 88, Manchester M60 1QD, UK

Received: 19 July 2004
Accepted: 16 October 2004

Abstract

In the framework of our narrow-band survey of Local Group galaxies, we present the results of the search for planetary nebulae (PNe) in three spheroidal companions to the Andromeda galaxy. We find 9 candidate PNe in NGC 147, 5 in NGC 185, and 75 in the ~0.4 square degree area searched around NGC 205, increasing the number of PNe known in these galaxies. It is shown that in the crowded regions of these galaxies continuum-subtracted images are more effective in detecting PNe than colour-colour diagrams obtained via automatic photometry. For NGC 205, the degree of contamination of PNe belonging to the halo of M 31 is estimated; taking it into account, 35 PNe within 1.5 tidal radii from the centre of NGC 205 have been used to build its PN luminosity function. Candidate PNe in NGC 185 are systematically brighter than those in NGC 147. Considering that star formation is thought to have been much stronger in NGC 185 than in NGC 147 in the last 3 Gyr, this might suggest that the bright end of the PN luminosity function is populated by relatively massive stars, as predicted by some recent theoretical models. This result, however, has to be taken with some caution, given the small PN population size of these galaxies and a rather incomplete knowledge of their star formation history.