Radio counterpart of the lensed submm emission in the cluster MS0451.6-0305: new evidence for the merger scenario

¹ Netherlands Foundation for Research in Astronomy (ASTRON), Postbus 2, 7990 AA Dwingeloo, The Netherlands e-mail: berciano@astro.rug.nl
² Kapteyn Astronomical Institute, University of Groningen, PO Box 800, 9700 AV, Groningen, The Netherlands
³ Leiden Observatory, PO Box 9513, 2300 RA, Leiden, The Netherlands
⁴ Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Mail number H39, PO Box 218, Hawthorn, Victoria 3122, Australia
⁵ Argelander-Institut für Astronomie (AIfA), University of Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁶ Laboratoire d'Astrophysique de Marseille, UMR 6110, CNRS-Université de Provence, 38 rue Frédéric Joliot-Curie, 13 388 Marseille Cedex 13, France
⁷ Dark Cosmology Centre, Niels Bohr Institute, University of Copenhagen, Juliane Maries Vej 30, 2100 Copenhagen, Denmark

Received: 16 July 2009
Accepted: 7 September 2009

Abstract

Context. SMM J04542-0301 is an extended (~) submm source located near the core of the cluster MS0451.6-0305. It has been suggested that part of its emission arises from the interaction between a LBG and two EROs at z ~ 2.9 that are multiply-imaged in the optical/NIR observations. However, the dramatic resolution difference between the sub-mm map and the optical/NIR images make it difficult to confirm this hypothesis.

Aims. In a previous paper, we reported the detection of 1.4 GHz continuum radio emission coincident with this sub-mm source using VLA archival data. To fully understand the relation between this radio emission, the sub-mm emission, and the optical/IR multiply-imaged sources, we have re-observed the cluster with the VLA at higher resolution.

Methods. The previous archival data has been re-reduced and combined with the new observations to produced a deep (~10 μJy beam^-1), high resolution (~) map centred on the cluster core. The strong lensing effect in the radio data has been quantified by constructing a new lens model of the cluster.

Results. From the high resolution map we have robustly identified six radio sources located within SMM J 04542-0301. The brightest and most extended of these sources (RJ) is located in the middle of the sub-mm emission, and has no obvious counterpart in the optical/NIR. Three other detections (E1, E2 and E3) seem to be associated with the images of one of the EROs (B), although the NIR and radio emission appear to originate at slightly different positions in the source plane. The last two detections (CR1 and CR2), for which no optical/NIR counterpart have been found, seem to constitute two relatively compact emitting regions embedded in a ~ extended radio source located at the position of the sub-mm peak. The presence of this extended component (which contributes 38% of the total radio flux in this region) can only be explained if it is being produced by a lensed region of dust obscured star formation in the center of the merger. A comparison between the radio and sub-mm data at the same resolution suggests that E1, E2, E3, CR1 and CR2 are associated with the sub-mm emission.

Conclusions. The radio observations presented in this paper provide strong observational evidence in favour of the merger hypothesis. However, the question if RJ is also contributing to the observed sub-mm emission remains open. These results illustrate the promising prospects for radio interferometry and strong gravitational lensing to study the internal structure of SMGs.