Spectroscopy of Circumnuclear Star Forming Regions in Early Type Spirals

M.V. CARDACI, G.F. HÄGELE, A.I. DÍAZ, E. TERLEVICH, R. TERLEVICH AND M. CASTELLANOS

Venecia, Italia

Congreso; From Stars to Galaxies: Building the pieces to build up the Universe; 2006

Universidad de Padova

We present spectroscopy observations of circumnuclear star forming regions (CNSFRs) in the galaxies: NGC 2903, NGC 3351 and NGC 3504, all of them of over solar metallicity according to standard empirical calibrations. Using data of moderate resolution a detailed determination of their abundances is made after careful subtraction of the very prominent underlying stellar absorption. A two-component (emission and absorption) Gaussian fit was performed in order to correct the Balmer lines for the underlying absorption. We have measured gas and stellar velocity dispersions in 5 CNSFRs and the nucleus of the barred spiral galaxy NGC3351. The stellar dispersions have been measured from high resolution spectra of the CaII \lambda\lambda 8494, 8542, 8662 A triplet lines (CaT), while the gas velocity dispersions have been measured by Gaussian fits to the H\beta 4861 A and [OIII] \lambda 5007 A lines on high dispersion spectra. Stellar velocity dispersions are between 46 and 76 km/s. Stellar and gas velocity dispersions are found to differ by about 20 km/s with the H\beta lines being narrower than both the stellar lines and the [OIII] \lambda 5007 A lines. However, the best Gaussian fits involved two different components for the gas: a "broad component" with a velocity dispersion similar to that measured for the stars, and a "narrow component" with a dispersion lower than the stellar one by about 30 km/s. When plotted in a [OIII]/H vs [NII]/H diagram, the two systems are clearly segregated with the narrow component having the lowest excitation and being among the lowest excitation line ratios detected within the SDSS dataset of starburst systems.