Circumnuclear star-forming regions in early type spiral galaxies: dynamical masses

G. F. HÄGELE; M. V. CARDACI; G. L. BOSCH; A. I. DÍAZ; E. TERLEVICH; R. TERLEVICH

La Plata

Congreso; V ADeLa: Astronomía Dinámica en Latinoamérica; 2012

UNLP - CONICET

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: NGC,2903, NGC,3310 and NGC,3351 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 4861A and to the [OIII]5007A lines. The CNSFRs, with sizes of about 100 to 150,pc in diameter, are seen to be composed of several individual star clusters with sizes between 1.5 and 6.2 pc on Hubble Space Telescope (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 1.9x10^8Msun and between 1.4x10^6 and 1.1x10^7Msun 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 25km/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.