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Astron. Astrophys. 330, 841-872 (1998)

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Bidimensional spectroscopy of double galaxies

II. Mkn 789, UGC 4085, UGC 3995 *

Eleni T. Chatzichristou 1, Christian Vanderriest 2 and Matthew Lehnert 1

1 Sterrewacht Leiden, Postbus 9513, 2300 RA Leiden, The Netherlands
2 DAEC, Observatoire de Paris-Meudon, 5 Place Jules Janssen, F-92195 Meudon Principal Cedex, France

Received 27 May 1997 / Accepted 24 September 1977


We present data obtained using the integral field spectrograph, SILFID, on the CFHT for three galaxies: Mkn 789, UGC 4085, UGC 3995. These systems are part of a larger ensemble of interacting/merger candidates, that were specifically chosen to have a range of nuclear activity, IR properties and strength of interaction. Unlike slit spectra, these data arrays provide a direct two-dimensional picture of the wavelength-dependent emission and absorption line properties of the galaxies. With the complement of optical photometry, we analyze for each object the kinematics of the gas component and the details of the ionization structure.

Mkn 789 is a recent merger with a fuzzy appearance whose infrared properties make it directly comparable to the powerful FIRGs. It is undergoing large scale star formation that powers a superwind seen as double peaked emission line profiles.

We do not find any evidence for UGC 4085 to be a merger, as the two central knots are elongated, showing typical HII region like spectra and the general velocity field indicates a smooth retrogradely rotating disk.

UGC 3995 is member of a closely interacting pair of galaxies that shows extended "cone"-like ionized gas morphology along a bar-like structure. Additional velocity components detected in the [FORMULA] profiles are interpreted as gas inflow along the bar, that may be responsible for activating the Seyfert nucleus. On the basis of these data we argue that the gas dynamics in the central (10-20 kpc) regions is dominated by the more energetic hydrodynamic processes rather than directly related to the merger itself.

Key words: galaxies: interactions – galaxies: Seyfert – galaxies: kinematics and dynamics – galaxies: individual: Mkn 789, UGC 4085, UGC 3995

* Based on observations collected with the Canada-France-Hawaii Telescope at Mauna Kea (Hawaii, USA)

Send offprint requests to: E. Chatzichristou

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© European Southern Observatory (ESO) 1998

Online publication: January 27, 1998