Circumnuclear star-forming regions in early type spiral galaxies:
  dynamical masses
  We present the measurements of gas and stellar velocity dispersions in 17
circumnuclear star-forming regions (CNSFRs) and the nuclei of three barred
spiral galaxies: NGC2903, NGC3310 and NGC3351 from high dispersion spectra. The
stellar dispersions have been obtained from the CaII triplet (CaT) lines at
8494, 8542, 8662A, while the gas velocity dispersions have been measured by
Gaussian fits to the Hbeta and to the [OIII]5007A\ lines. The CNSFRs, with
sizes of about 100 to 150pc in diameter, are seen to be composed of several
individual star clusters with sizes between 1.5 and 6.2pc on HST images. Using
the stellar velocity dispersions, we have derived dynamical masses for the
entire star-forming complexes and for the individual star clusters. Values of
the stellar velocity dispersions are between 31 and 73 km/s. Dynamical masses
for the whole CNSFRs are between 4.9x10^6 and 1.9x10^8 Mo and between 1.4x10^6
and 1.1x10^7 Mo for the individual star clusters. We have found indications for
the presence of two different kinematical components in the ionized gas of the
regions. The narrow component of the two-component Gaussian fits seem to have a
relatively constant value for all the studied CNSFRs, with estimated values
close to 25 km/s. This narrow component could be identified with ionized gas in
a rotating disc, while the stars and the fraction of the gas (responsible for
the broad component) related to the star-forming regions would be mostly
supported by dynamical pressure.
