The young stellar population at the center of NGC 205
Bellazzini, M.; Saviane, I.; Monaco, L.; Galleti, S.; Federici, L.; Fusi Pecci, F.; Perina, S.; Buzzoni, A.
Chile, Italy
Abstract
Context: NGC 205 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 NGC 205 and M 31.
Aims: The star formation history in the central 30´´ (~120 pc) around the NGC 205 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 SF rate.
Results: Our photometry reveals a previously undetected blue plume of young stars clearly distinguishable down to I≃ 26. Our analysis suggests that 1.9 × 105 M_⊙ were produced between approximately 62 Myr and 335 Myr ago in the NGC 205 inner regions, with a latest minor episode occurring ~25 Myr ago. This implies a star formation rate of ~7× 10-4 M_⊙/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 ~300 Myr. Rather, a constant SF may be consistent with NGC 205 being on its first interaction with M 31.