Abstract
We have measured gas and stellar velocity dispersions in five circumnuclear star-forming regions (CNSFRs) and the nucleus of the barred spiral galaxy NGC 3351. The stellar dispersions have been obtained from high-resolution spectra of the Ca II triplet (CaT) lines at λλ8494, 8542, 8662 A, while the gas velocity dispersions have been measured by Gaussian fits to the Hβ λ4861 A line on high-dispersion spectra. The CNSFRs, with sizes of about 100 to 150pc in diameter, are seen to be composed of several individual star clusters with sizes between 1.7 and 4.9 pc on a Hubble Space Telescope (HST) image. 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 39 and 67 km s -1 . Dynamical masses for the whole CNSFRs are between 4.9 x 106 and 4.3 x 10 7 M ⊙ and between 1.8 and 8.7 x 10 6 M ⊙ for the individual star clusters. Stellar and gas velocity dispersions are found to differ by about 20kms -1 with the Hβ lines being narrower than both the stellar lines and the [O III]λ5007 A lines. We have found indications for the presence of two different kinematical components in the ionized gas of the regions. The radial velocity curve shows deviation from circular motions for the ionized hydrogen consistent with its infall towards the central regions of the galaxy at a velocity of about 25 km s -1 . To disentangle the origin of these two components it will be necessary to map these regions with high spectral and spatial resolution and much better signal-to-noise ratio in particular for the O 2+ lines.
Highlights
The bulges of some nearby spiral galaxies show intense star-forming regions located in a roughly annular pattern around their nuclei
Masses derived from the Hβ velocity dispersion under the assumption of a single component for the gas would have been underestimated by factors of between approximately 2 and 4
The stellar dispersions have been measured from high-resolution spectra of the Ca II triplet (CaT) lines at λλ8494, 8542, 8662 Å, while the gas velocity dispersions have been measured by Gaussian fits to the Hβ λ4861 Å line on high dispersion spectra
Summary
The bulges of some nearby spiral galaxies show intense star-forming regions located in a roughly annular pattern around their nuclei. Journal compilation C 2007 RAS sample of 35 Seyfert 2 galaxies, find that about 40 per cent of them show unambiguous evidence of circumnuclear star formation within 300 pc of the nucleus and that these star-forming regions contribute about 30 to 50 per cent to the Hβ total emission of the central zone. These CNSFRs, with sizes going from a few tens to a few hundreds of parsec The luminosities of CNSFRs are rather large with absolute visual magnitudes (Mv) between −12 and −17 and Hα luminosities between 2 × 1038
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
