Implications of the kinematical structure of circumnuclear star-forming regions on their derived properties

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

MONTHLY NOTICES OF THE ROYAL ASTRONOMICAL SOCIETY

WILEY-BLACKWELL PUBLISHING, INC

Lugar: Londres; Año: 2013 vol. 432 p. 810 - 821

0035-8711

We review the results of high dispersion spectroscopy of 17circumnuclear star-forming regions (CNSFRs) in 3 nearby early spiral galaxies, NGC2903, NGC3310 and NGC3351. We find that single Gaussian fitting to the Hbeta and [OIII]5007 line profiles results in velocity dispersions around 32 km/s and 52km/s, respectively, while the IR CaII triplet cross-correlation technique provides stellar velocity dispersion values close to 50km/s.Even though multiple kinematical components are present, the relation between gas velocity dispersion and Balmer emission line luminosity (L-sigma relation) reproduces the correlation for disk giant HII regions albeit with a larger scatter. The scatter in the L-sigma relation is considerably reduced when theoretical evolutionary corrections are applied suggesting that an age range is present in the sample of CNSFRs.To analyse the observed complex profiles, we performed multiple Gaussian component fits to the Hbeta and [OIII]5007 lines obtaining optimal fits with two Gaussians of different width. These best fits indicate that the narrower component has average velocity dispersion close to 23km/s while the broader component shows average values in the range 50-60km/s for both lines, close to the observed stellar velocity dispersions. The fl uxes of the broad and narrow Hbeta components are similar. This is not the case for [OII]5007 for which the broad components have higher fl uxes than the narrow ones, thus producing a clear segregation in their [Oiii]/H ratios.We suggest a possible scenario for understanding the behaviour of CNSFRs in the L-sigma and sigma_gas-sigma_star diagrams involving an inner gaseous disk responsible for the narrow component of the emission lines.Our main conclusion is that the presence of different kinematical components with similar total  fluxes in the emission line spectrum of CNSFRs raises important doubts regarding properties of the ionized gas derived from global line ratios obtained with low resolution spectroscopy in star-forming regions in the central regions of early type galaxies. Given the ubiquity of these star-forming systems, ionized gas analyses should be done preferably from high dispersion spectra with high spatial resolution.