Letter to the Editor

First detection of a minor merger at z ~ 0.6

¹ ESO, Karl-Schwarzschild-Strasse 2, 85748 Garching bei München, Germany e-mail: mpuech@eso.org
² GEPI, Observatoire de Paris, CNRS, University Paris Diderot, 5 place Jules Janssen, 92190 Meudon, France

Received: 7 September 2007
Accepted: 25 October 2007

Abstract

Context.Numerical simulations predict that minor mergers are an important channel for the mass assembly of galaxies. However, minor mergers are relatively difficult to detect using imaging, especially at high redshift. While such events are much less violent than major mergers, they can nevertheless leave several features on the kinematical structures of remnant galaxies which could be detected using 3D spectroscopy.

Aims.We present the first direct detection of a minor merger in a z ~0.6 galaxy. Such events could indeed be good candidates to explain the kinematics of perturbed rotating disks observed with GIRAFFE at z ~0.6.

Methods.We present photometric and kinematical evidence of such an event in a combined analysis of three-band HST/ACS imaging and VLT/GIRAFFE 2D-kinematics.

Results.Using these data, we are able to demonstrate that a minor merger of a relatively small satellite (mass ratio ~1:18) is occurring in this galaxy. We also derive a total SFR of ~21 /yr.

Conclusions.Minor mergers could be one of the physical processes explaining the kinematics of perturbed rotating disks, which represent ~25% of emission line intermediate mass galaxies at z ~0.6. 3D spectroscopy appears to be a very good tool to identify minor mergers in distant (and local) galaxies.