- [*] CO-bandhead spectroscopy of IC 342: mass and age of the nuclear star
- Boeker T., van der Marel R.P., Vacca W.
- AJ, 118, 831-842, 1999
- © 1999. The American Astronomical Society.
All Rights Reserved.
this paper in the ADS
We have used the NASA Infra-Red Telescope Facility (IRTF) to observe
the nuclear stellar cluster in the nearby, face-on, giant Scd spiral
IC 342. From high resolution (R = 21500) spectra at the 12CO (2-0)
bandhead at 2.3 micron we derive a line-of-sight stellar velocity
dispersion sigma = (33 +- 3) km/s. 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
times 10^6 Msun.
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 discuss the
implications of this result on possible scenarios for the frequency of
nuclear starbursts and their impact on secular evolution of spiral
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 March 30, 1999.
Roeland van der Marel,