Determining the morpho-kinematic properties of a face-on merger at z ~ 0.7

¹ GEPI, Observatoire de Paris, UMR 8111 CNRS, Université Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France
² Escuela Superior de Física y Matemáticas, Instituto Politécnico Nacional (ESFM-IPN), U.P. Adolfo López Mateos, edifico 9, Zacatenco, 07730 Mexico City, Mexico e-mail: isaura.fuentes@obspm.fr; isaura@esfm.ipn.mx
³ National Astronomical Observatories, Chinese Academy of Sciences, 20A Datun Road, Chaoyang District, Beijing 100012, PR China
⁴ Institut d'Astrophysique de Paris, UMR 7095 CNRS, Université Pierre et Marie Curie, 98bis Bd Arago, 75014 Paris, France
⁵ CENTRA, Instituto Superior Técnico, Av. Rovisco Pais 1049-001 Lisboa, Portugal

Received: 18 August 2009
Accepted: 13 January 2010

Abstract

Context. At intermediate redshifts, many galaxies seem to have experienced an interaction. It is not always straightforward to determine what type of encounter or perturbation is observed, nor the outcome of this event. In some cases, only the use of both morphological and kinematical information can determine the true configuration of an encounter at intermediate redshift.

Aims. We present the morphological and kinematical analysis of a system at z = 0.74 to understand its configuration, interacting stage, and evolution.

Methods. Using the integral field spectrograph GIRAFFE, long-slit spectroscopy by FORS2, direct optical images from the HST-ACS, and ISAAC near-infrared images, we determine the morphology of this system, its star-formation history, and its extended kinematics to propose a possible configuration for the system. Numerical simulations are used to test different interacting scenarii.

Results. We identify this system to be a face-on disk galaxy with a very bright bar that is interacting with a smaller companion such that the galaxy and the companion have a mass ratio of 3:1. The relevance of kinematical information and the constraints that it imposes on the interpretation of the observations of distant galaxies are particularly greater in this case.

Conclusions. This object represents one of the clearest examples of how one can misinterpret morphology in the absence of kinematical information.