Kinematics of gas and stars in circumnuclear star-forming regions of early type spirals

We present high resolution (R 20000) spectra in the blue and the far red of cicumnuclear star-forming regions (CNSFRs) in three early type spirals (NGC3351, NGC2903 and NGC3310) which have allowed the study of the kinematics of stars and ionized gas in these structures and, for the first time, the derivation of their dynamical masses for the first two. In some cases these regions, about 100 to 150 pc in size, are seen to be composed of several individual star clusters with sizes between 1.5 and 4.9 pc estimated from Hubble Space Telescope (HST) images. The stellar dispersions have been obtained from the Calcium triplet (CaT) lines at λλ 8494,8542,8662 Å, while the gas velocity dispersions have been measured by Gaussian fits to the Hβ and [OIII]λλ 5007 Ålines on the high dispersion spectra. Values of the stellar velocity dispersions are between 30 and 68 km/s. We apply the virial theorem to estimate dynamical masses of the clusters, assuming that systems are gravitationally bounded and spherically symmetric, and using previously measured sizes. The measured values of the stellar velocity dispersions yield dynamical masses of the order of 10 to 10 solar masses for the whole CNSFRs. Stellar and gas velocity dispersions are found to differ by about 20 to 30 km/s with the Hβ emission lines being narrower than both the stellar XMM-Newton Science Operations Center, ESAC, ESA, POB 78, E-28691 Villanueva de la Cañada, Madrid, Spain. Research Affiliate at IoA.