A&A 485, 695-705 (2008)
On the morphology of sigma-drop galaxiesS. Comerón1, J. H. Knapen1, and J. E. Beckman1, 2
1 Instituto de Astrofísica de Canarias, 38200 La Laguna, Spain
2 Consejo Superior de Investigaciones Científicas, Spain
Received 28 November 2007 / Accepted 28 April 2008
Context. Local reductions of the stellar velocity dispersion in the central regions of galaxies are known as sigma-drops (-drops). Knowing the origin of these features can lead to better understanding of inner galactic dynamics.
Aims. We present a sample of 20 -drop galaxies matched with a control sample of galaxies without -drop in order to search for correlations between -drops and the properties, primarily morphological, of the nuclear zones and discs of their host galaxies.
Methods. We study the dust and H distribution at 0.1 arcsec scale, using Hubble Space Telescope imaging, in the circumnuclear zones of the two samples of galaxies, searching for differences and trying to establish a link between the nuclear kinematics and the host morphology. We have also considered the CO and H I emission of the galaxies and their luminosity profiles.
Results. We classify the two samples following both morphological parameters and the luminosity profiles. We find a larger fraction of nuclear dust spirals and H rings in the -drop sample. We also find that the fraction of Seyfert galaxies in the -drop sample is bigger than that of LINERs and that the reverse is true for the control sample.
Conclusions. Our findings are evidence that a -drop is very probably due to inflow-induced star formation in a dynamically cool disc, or in a gas ring, shock focused by an inner Lindblad resonance above a certain critical density level. The same mechanism that feeds the nuclear ring or the nuclear disc is probably reponsible for the higher rate of Seyfert galaxies among the -drop hosts.
Key words: Galaxy: kinematics and dynamics -- galaxies: nuclei -- galaxies: statistics
© ESO 2008