We have used the NASA Infrared Telescope Facility (IRTF) to observe the nuc
lear stellar cluster in the nearby, face-on, giant Scd spiral IC 342. From
high-resolution (lambda/Delta lambda = 21,500) spectra of the (CO)-C-12 (2-
0) band head at 2.3 mu m, we derive a line-of-sight stellar velocity disper
sion sigma = (33 +/- 3) km s(-1).
To interpret this observation we construct dynamical models based on the Je
ans equation for a spherical system. The light distribution of the cluster
is modeled using an archival Hubble Space Telescope (HST) V-band image and
a new ground-based K-band image. Under the assumption of an isotropic veloc
ity distribution, the observed kinematics imply a K-band mass-to-light rati
o M/L-K = 0.05, and a cluster mass M approximate to 6 x 10(6) M-circle dot.
We compare the derived 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 10(6.8-7.8) yr. Although this result depe
nds somewhat on a number of uncertainties in the modeling (e.g., the assume
d extinction along the line of sight toward the nucleus, the initial mass f
unction of the stellar population model, and the velocity dispersion anisot
ropy of the cluster), none of the model parameters can be plausibly modifie
d to yield a significantly larger age. Also, the inferred age is consistent
with that found in our previous study based on the near-infrared absorptio
n-line equivalent widths of the cluster (Boker, Forster-Schreiber, & Genzel
).
Recent HST observations of large samples of spiral galaxies have shown that
nuclear stellar clusters are very common in intermediate- to late-type spi
rals. The cluster in IC 342 is more luminous than the clusters found in mos
t other nearby spiral galaxies. If the nuclear stellar clusters in spiral g
alaxies all have a mass similar to that of the cluster in IC 342, then stel
lar population synthesis models indicate a median age for these clusters of
several Gyr. This may be consistent with a scenario in which each spiral g
alaxy has only one episode of nuclear star cluster formation. On the other
hand, the incidence of young nuclear star clusters may be high enough to in
dicate that the formation of these clusters is a recurring phenomenon. Age
and population studies for a larger sample of galaxies are necessary to dis
tinguish between these scenarios and to determine how these nuclear stellar
clusters are related to the secular evolution of their environment.
As a by-product of our analysis, we infer that IC 342 cannot have any centr
al black hole more massive than 5 x 10(5) M-circle dot. This is similar to
6 times less massive than the black hole inferred to exist in our Galaxy, c
onsistent with the accumulating evidence that galaxies with less massive bu
lges harbor less massive black holes.