Radio counterpart of the lensed sub-mm emission in the cluster
  MS0451.6-0305: new evidence for the merger scenario
  SMM J04542-0301 is an extended (~1 arcmin) sub-mm 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. However, the dramatic resolution difference between the
sub-mm map and the optical/NIR images make it difficult to confirm this
hypothesis. In this paper, we present a deep (~ 10 microJy/beam), high
resolution (~2 arcsec) 1.4 GHz radio map of the cluster core, in which we have
identified 6 sources located within SMM J04542-0301. The strong lensing effect
in the radio data has been quantified by constructing a new lens model of the
cluster. 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. 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 ~5 arcsec extended radio source located
at the position of the sub-mm peak. The presence of this extended component 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. The radio observations provide strong
observational evidence in favor 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.
