Astronomy & Astrophysics

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Issue		A&A Volume 431, Number 3, March I 2005
Page(s)		L21 - L24
Section		Letters
DOI		10.1051/0004-6361:200500002

A&A 431, L21-L24 (2005)
DOI: 10.1051/0004-6361:200500002

Letter

Gravitationally lensed radio emission associated with SMM J16359+6612, a multiply imaged submillimeter galaxy behind A 2218

M. A. Garrett¹, K. K. Knudsen² and P. P. van der Werf³

¹ Joint Institute for VLBI in Europe, Postbus 2, 7990 AA, Dwingeloo, The Netherlands
e-mail: garrett@jive.nl
² Max-Planck-Institute für Astronomie, Königstuhl 17, 69117 Heidelberg, Germany
³ University of Leiden, Department of Astronomy, PO Box 9513, 2300 RA Leiden, The Netherlands

(Received 7 December 2004 / Accepted 8 January 2005 )

Abstract
We report the detection of discrete, lensed radio emission from the multiply imaged, z=2.516 submillimetre selected galaxy, SMM J16359+6612. All three images are detected in deep WSRT 1.4 GHz and VLA 8.2 GHz observations, and the radio positions are coincident with previous sub-mm SCUBA observations of this system. This is the widest separation lens system to be detected in the radio so far, and the first time that multiply imaged lensed radio emission has been detected from a star forming galaxy - all previous multiply-lensed radio systems being associated with radio-loud AGN. Taking into account the total magnification of ~ 45, the WSRT 1.4 GHz observations suggest a star formation rate of ~ $500~M_{\odot}$ yr ^-1. The source has a steep radio spectrum $\alpha \sim -0.7$ and an intrinsic flux density of just 3 microJy at 8.2 GHz. Three other SCUBA sources in the field are also detected by the WSRT, including SMM J16359+66118, a singly imaged (and magnified) arclet at z=1.034. Higher resolution radio observations of SMM J16359+6612 (and other highly magnified star forming galaxies) provide a unique opportunity to study the general properties and radio morphology of intrinsically faint, distant and obscured star forming galaxies. They can also help to constrain the technical specification of next generation radio telescopes, such as the Square Kilometre Array.

Key words: gravitational lensing -- galaxies: starburst -- radio continuum: galaxies

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