2001ApJ...556..801L -
Astrophys. J., 556, 801-812 (2001/August-1)
Structure and mass of a young globular cluster in NGC 6946.
LARSEN S.S., BRODIE J.P., ELMEGREEN B.G., EFREMOV Y.N., HODGE P.W. and RICHTLER T.
Abstract (from CDS):
Using the Wide Field Planetary Camera 2 on board the Hubble Space Telescope, we have imaged a luminous young star cluster in the nearby spiral galaxy NGC 6946. Within a radius of 65 pc, the cluster has an absolute visual magnitude, MV=-13.2, comparable to the most luminous young ``super star clusters'' in the Antennae merger galaxy. UBV colors indicate an age of about 15 Myr. The cluster has a compact core (radius ∼1.3 pc) surrounded by an extended envelope with a power-law luminosity profile. The outer parts of the cluster profile gradually merge with the general field, making it difficult to measure a precise half-light radius Re, but we estimate Re∼13 pc. Combined with population synthesis models, the luminosity and age of the cluster imply a mass of 8.2x105 M☉ for a Salpeter initial mass function (IMF) extending down to 0.1 M☉. If the IMF is lognormal below 0.4 M☉, then the mass decreases to 5.5x105 M☉. Depending on model assumptions, the central density of the cluster is between 5.3x103 and 1.7x104 M☉.pc–3, comparable to other high-density star-forming regions. We also estimate a dynamical mass for the cluster using high-dispersion spectra from the HIRES spectrograph on the Keck I telescope. The HIRES data indicate a velocity dispersion of 10.0±2.7 km.s–1 and imply a total cluster mass within 65 pc of 1.7±0.9x106 M☉. Comparing the dynamical mass with the mass estimates based on the photometry and population synthesis models, we find that the mass-to-light ratio is at least as high as for a Salpeter IMF extending down to 0.1 M☉, although a turnover in the IMF at 0.4 M☉ is still possible within the ∼1 σ errors. The cluster will presumably remain bound, evolving into a globular cluster-like object.
Abstract Copyright:
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Journal keyword(s):
Galaxies: Individual: NGC Number: NGC 6946 - Galaxies: Star Clusters
CDS comments:
The cluster in the title is [L99] n6946-1447, p. 802 : NGC 1569A = [W91] A, NGC 1705A = MMT A
Simbad objects:
33
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