The morphology of minor axis gaseous outflows in edge-on Seyfert galaxies ^*,**

¹ SUPA, School of Physics and Astronomy, University of St. Andrews, North Haugh, KY16 9SS St. Andrews, UK e-mail: tr9@st-andrews.ac.uk
² Space Telescope Science Institute, 3700 San Martin Drive, Baltimore, MD 21218, USA e-mail: marel@stsci.edu
³ Department of Astronomy, University of Florida, 211 Bryant Space Science Center, PO Box 112055, Gainesville, FL 32611, USA e-mail: jrossa@astro.ufl.edu
⁴ Astronomisches Institut, Ruhr-Universität Bochum, Universitätsstrasse 150/NA7, 44780 Bochum, Germany e-mail: bomans@astro.rub.de

Received: 18 April 2006
Accepted: 20 December 2006

Abstract

Context.Spiral galaxies often have extended outflows that permeate beyond the region of the disk. Such outflows have been seen both in starburst galaxies, actively star forming galaxies and galaxies with an AGN. In the latter galaxies it is unknown whether the large-scale outflows are driven by star formation activity or purely by the active nucleus.

Aims.The aim of our investigation is to study the frequency of extended minor-axis outflows in edge-on Seyfert galaxies to investigate the role of the AGN, the circumnuclear environment and star formation activity within the disk regions, and their importance for IGM enrichment on large scales.

Methods.We obtained optical narrowband imaging observations of a distance limited, northern hemisphere sample of 14 edge-on Seyfert spiral galaxies. Because of the distance-limited nature of the sample, it is restricted to relatively low-luminosity Seyfert galaxies. The data were obtained with BUSCA attached to the 2.2 m telescope at the Calar Alto observatory. Narrowband imaging in two different ionizational stages (Hα and [O iii] ) was performed to attempt a discrimination between processes associated with the active nucleus and those connected to star forming activity within the disk. The median 3-σ sensitivities for detection of high-latitude extended emission in the sample galaxies are  erg s^-1 cm^-2 arcsec^-2 for the Hα images and  erg s^-1 cm^-2 arcsec^-2 for the [O iii] images. We use the data to study the distribution of extraplanar emission with respect to the AGN and the underlying disk H ii regions.

Results.The Hα morphology of the Seyfert galaxies is usually complex, but only in three out of 14 galaxies did we find evidence for minor axis disk outflows. At the sensitivity of our observations [O iii]  emission is generally detected only in the nuclear region. For Ark 79 we present the first evidence of a secondary nuclear component, best visible in the [O iii] image, which has a linear separation from the primary nucleus of about 850 pc.

Conclusions.Overall, our results show that extraplanar emission of similar brightness and extent as in the previously known cases of NGC 3079 and NGC 4388 is not common in Seyfert galaxies of otherwise similar properties. Comparison with our previous results shows that for nearby edge-on spiral galaxies star formation may be a more powerful mechanism for producing DIG than AGN activity. While in general AGN activity undoubtedly plays some role in driving minor-axis outflows, this probably requires higher AGN luminosities than are encountered in our small distance-limited sample.