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

Abstract

Context. SMM J04542-0301 is an extended (∼1 ) 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 multiplyimaged 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 (∼2 ) 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 ∼5 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.

The matter distribution inz~ 0.5 redshift clusters of galaxies

“…Interestingly, a SCUBA detection of an extended source in the cluster centre led to the identification of an ERO pair, triple imaged (Chapman et al 2002;Takata et al 2003;Berciano Alba et al 2010). These features point towards the bright central galaxy as the centre of the mass distribution.…”

Cosmic evolution of submillimeter galaxies and their contribution to stellar mass assembly

“…Such extreme SFRs likely result from major mergers (e.g. Chapman et al 2004;Swinbank et al 2004;Greve et al 2005;Tacconi et al 2006Tacconi et al , 2008Younger et al 2007Younger et al , 2008Berciano Alba et al 2010;Narayanan et al 2009Narayanan et al , 2010 and cannot be sustained for a long period (after a few hundred Myr at most the gas reservoir should be depleted; see Greve et al 2005;Hainline et al 2006).…”

Strong-lensing analysis of a complete sample of 12 MACS clusters at z > 0.5: mass models and Einstein radii

“…The galaxy cluster MACS J0454.1−0300 ( z = 0.538, also known as MS 0451.6−0305) has been subject to extensive study due to its high X‐ray luminosity, strong SZ effect, and high redshift (e.g. Ellingson et al 1998; Molnar et al 2002; Laroque et al 2003; Geach et al 2006), and is known to host various lensed submillimetre sources with radio counterparts (Takata et al 2003; Borys et al 2004; Berciano Alba et al 2007, 2010), which we incorporate in our analysis below. Previous strong‐lensing models of this cluster were introduced by Borys et al (2004) and Berciano Alba et al (2010) with similar symmetry as our model.…”

“…In the case of MACS J1149.5+2223 (Zitrin & Broadhurst 2009), a background spiral galaxy at z = 1.49 (Smith et al 2009) has been shown to be multiply‐lensed into several very large images, requiring a very shallow, unrelaxed central mass distribution. Another large multiply‐lensed submillimetre source at a redshift of z ≃ 2.9 has been identified in MACS J0454.1−0300 (also referred to as MS 0451.6−0305; Takata et al 2003; Borys et al 2004; Berciano Alba et al 2007, 2010), MACS J0025.4−1222 was found to be a ‘bullet cluster’ like (Bradač et al 2008b) and other MACS clusters have been recently used for an extensive arc statistics study (Horesh et al 2010).…”