- [*] Nuclear Star Clusters in Bulgeless Galaxies
- Walcher C.J., Haering N., Boeker T., Rix H.-W.,
van der Marel R.P., Gerssen J., Ho L., Shields J.
- in Carnegie Observatories Astrophysics Series,
Vol. 1: Coevolution of Black Holes and Galaxies, ed. L. C. Ho
(Pasadena: Carnegie Observatories, http://www.ociw.edu/ociw/symposia/series/symposium1/proceedings.html), in press, 2003
Centers of spiral galaxy bulges are very special in terms of their
dynamics and star formation history. We investigate whether the
centers of bulge-less galaxies are as unique in their structure and
stellar populations. Our HST imaging survey of very late-type,
bulge-less (Sd) galaxies has revealed unusually bright, nuclear star
clusters at their photometric center in 75 percent of the cases. We
have obtained high-resolution spectra with UVES at the VLT for 10 of
those objects. We find that the majority of the clusters are younger
than 1 Gyr. The masses of the clusters as determined from the velocity
dispersion range between 10^6 and 10^8 solar masses and are typically
one order of magnitude higher than would be expected from stellar
synthesis models. We interpret this as an underlying population of
older generations of stars that have already faded with time and thus
do not show up in the spectrum. Consequently nuclear cluster formation
is a repetitive event in very late type galaxies, which can contribute
to the build-up of bulges.
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Last modified March 30, 2003.
Roeland van der Marel,