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| Home > Public Information > Scientific Highlights > 1999 |
DISCOVERY OF YOUNG
STARS IN NGC 185, A DWARF ELLIPTICAL GALAXY
JKT+CCD Since the early work of Baade elliptical galaxies were considered to be essentially old, coeval systems with ages comparable to those of Milky Way Population II globular clusters. In the light of recent data, however, there is evidence that the majority of the Local Group dwarf elliptical (dE) galaxies have undergone recent star formation activity. The study of the stellar content of dE galaxies by means of their color-magnitude diagrams provides the most direct method of establishing whether they have had star formation episodes since the initial primeval event and even to locate in time, in a more precise way, that initial star formation event. The Local Group dE galaxies offer a unique opportunity to study their evolution in detail by this means. NGC 185 is a dE companion of the Andromeda
galaxy. The presence of a dozen of bright, blue stars and two conspicuous
dust patches in the central area of NGC 185 was firstly noted by Baade
in 1951. These "Population I" features indicated that NGC 185 did not fit
the concept of dE galaxies as pure Population II systems. For this reason,
NGC 185 was classified as a peculiar dE galaxy.
A recent study of NGC 185 shows that the luminous, blue stars discovered by Baade are in fact young stellar clusters at the distance of the galaxy. Furthermore, the recent analysis of the star formation history of NGC 185 using synthetic color-magnitude diagrams shows that the bulk of the stars were formed in an early epoch of its evolution. After that, star formation proceeded at a low rate until the recent past, the age of the most recent traces of star formation activity detected in the galaxy being some 100 Myr. These conclusions rule out the possibility of NGC 185 being an old galaxy formed by Population II stars only. Some references:
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