The H I content of the advanced merger NGC 4441

¹ University of Bochum, Department of Astronomy, 44780 Bochum, Germany
² Astron, 7990AA Dwingeloo, The Netherlands e-mail: manthey@astron.nl
³ Onsala Space Observatory, Chalmers University of Technology, 439 92 Onsala, Sweden
⁴ Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700AV Groningen, The Netherlands

Received: 2 April 2007
Accepted: 3 April 2008

Abstract

Context. NGC 4441 is a candidate for a merger between a spiral and an elliptical galaxy (S+E merger), because it shows typical tidal structures such as an optical tail and two shells. With a far-infrared luminosity of ~510⁹ this galaxy belongs to the class of moderate luminosity mergers, in which the merging process induces (if at all) only a moderate starburst.

Aims. The study of the atomic gas content allows us to investigate the merger history and the impact on the star formation. In particular, it is not clear from simulations whether an S+E merger leads to a gas concentration in the nucleus, resulting in a starburst, or whether the gas is spread out and therefore too diffuse for new star forming regions.

Methods. We used the Westerbork Radio Synthesis Telescope to observe the properties of the H I. By using this interferometer, we are able to study the large-scale H I distribution and kinematics with high spatial and velocity resolution.

Results. We found two H I tails extending out to more than 40 kpc. In a central disc, the gas shows a fairly regular rotation pattern indicating that the gas started to settle after the merger. The total H I mass adds up to 1.510⁹ . By comparing the high resolution H I maps with deep optical images, differences between the stellar and gaseous tidal features are apparent, which indicates an S+E merger origin.