The young stellar population at the center of NGC?205

摘要

Context. NGC205 is a peculiar dwarf elliptical galaxy hosting in its center a population of young blue stars. Their origin is still matter of debate, the central fresh star formation activity possibly being related to dynamical interactions between NGC205 and M31. Aims. The star formation history in the central30(120pc) around the NGC205 central nucleus is investigated in order to obtain clues to the origin of the young stellar population. Methods. Deep HST/ACS CCD photometry is compared with theoretical isochrones and luminosity functions to characterize the stellar content of the region under study and compute the recent SFrate. Results. Our photometry reveals a previously undetected blue plume of young stars clearly distinguishable down to .Our analysis suggests that were produced between approximately 62Myr and 335Myr ago in the NGC205 inner regions, with a latest minor episode occurring 25Myr ago. This implies a star formation rate of /yr over this period. Conclusions. The excellent fit of the observed luminosity function of young main sequence stars obtained with a model having a constant star formation rate argues against a tidally triggered star formation activity over the last 300Myr. Rather, a constant SF may be consistent with NGC205 being on its first interaction with M31. Key words: galaxies: evolution - galaxies: dwarf - galaxies: individual: NGC205 dE