We have obtained high-dispersion spectra for four massive star clusters in the dwarf irregular galaxies NGC 4214 and NGC 4449 , using the HIRES spectrograph on the Keck I telescope .
Combining the velocity dispersions of the clusters with structural parameters and photometry from images taken with the Hubble Space Telescope , we estimate mass-to-light ratios and compare these with simple stellar population ( SSP ) models in order to constrain the stellar mass functions ( MFs ) of the clusters .
For all clusters we find mass-to-light ratios which are similar to or slightly higher than for a Kroupa MF , and thereby rule out any MF which is deficient in low-mass stars compared to a Kroupa-type MF .
The four clusters have virial masses ranging between 2.1 \times 10 ^ { 5 } \mbox { $M _ { \odot } $ } and 1.5 \times 10 ^ { 6 } \mbox { $M _ { \odot } $ } , half-light radii between 3.0 and 5.2 pc , estimated core densities in the range 2 \times 10 ^ { 3 } \mbox { $M _ { \odot } $ } { pc } ^ { -3 } to 2 \times 10 ^ { 5 } \mbox { $M _ { \odot } $ } { pc } ^ { -3 } and ages between 200 Myr and 800 Myr .
We also present new high-dispersion near-infrared spectroscopy for a luminous young ( \sim 15 Myr ) cluster in the nearby spiral galaxy NGC 6946 , which we have previously observed with HIRES .
The new measurements in the infrared agree well with previous estimates of the velocity dispersion for this cluster , yielding a mass of about 1.7 \times 10 ^ { 6 } \mbox { $M _ { \odot } $ } .
The properties of the clusters studied here are all consistent with the clusters being young versions of the old globular clusters found around all major galaxies .