EDP Sciences
Free access
Volume 485, Number 3, July III 2008
Page(s) 695 - 705
Section Extragalactic astronomy
DOI http://dx.doi.org/10.1051/0004-6361:20079161
Published online 06 May 2008

A&A 485, 695-705 (2008)
DOI: 10.1051/0004-6361:20079161

On the morphology of sigma-drop galaxies

S. Comerón1, J. H. Knapen1, and J. E. Beckman1, 2

1  Instituto de Astrofísica de Canarias, 38200 La Laguna, Spain
    e-mail: sebastien@iac.es
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 ($\sigma$-drops). Knowing the origin of these features can lead to better understanding of inner galactic dynamics.
Aims. We present a sample of 20 $\sigma$-drop galaxies matched with a control sample of galaxies without $\sigma$-drop in order to search for correlations between $\sigma$-drops and the properties, primarily morphological, of the nuclear zones and discs of their host galaxies.
Methods. We study the dust and H$\alpha$ 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$\alpha$ rings in the $\sigma$-drop sample. We also find that the fraction of Seyfert galaxies in the $\sigma$-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 $\sigma$-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 $\sigma$-drop hosts.

Key words: Galaxy: kinematics and dynamics -- galaxies: nuclei -- galaxies: statistics

© ESO 2008