[*] High-resolution CO-bandhead spectroscopy of IC 342: mass and age of the nuclear star cluster

Boeker T., van der Marel R.P., Vacca W.

BAAS, 31, 3, 831, 1999 (AAS Meeting 194, 07.02)

© 1999. The American Astronomical Society. All Rights Reserved.

• Poster Paper (.ps 1760 kb) (.ps.gz 776 kb) [note: may not show properly in ghostview, but should print OK]

To interpret this observation we construct dynamical models based on the Jeans equation for a spherical system. The light distribution of the cluster is modeled using an isophotal analysis of an HST V-band image from the HST Data Archive, combined with new ground-based K-band imaging. Under the assumption of an isotropic velocity distribution, the observed kinematics imply a K-band mass-to-light ratio M/L_K = 0.05, and a cluster mass M ~ 6 million solar masses. We model the mass-to-light ratio with the `starburst99' stellar population synthesis models of Leitherer and collaborators, and infer a best-fitting cluster age in the range 63-630 Myears. Although this result depends somewhat on a number of uncertainties in the modeling (e.g., the assumed extinction along the line-of-sight towards the nucleus, the IMF of the stellar population model, and the velocity dispersion anisotropy of the cluster), none of these can be plausibly modified to yield a significantly larger age. We will discuss the implications of this result on scenarios of cluster formation in the nuclei of spiral galaxies.

As a byproduct of our analysis, we infer that IC 342 cannot have any central black hole more massive than 0.5 million solar masses. This is ~ 6 times less massive than the black hole inferred to exist in our Galaxy, consistent with the accumulating evidence that galaxies with less massive bulges harbor less massive black holes.

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Last modified May 4, 1999.
Roeland van der Marel, marel@stsci.edu.
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