A Hubble Space Telescope lensing survey of X-ray luminous galaxy clusters -: III.: A multiply imaged extremely red galaxy at z=1.6

We present near-infrared spectroscopy and Hubble Space Telescope (HST) imaging of galaxy J003707+0909.5, the brightest of three gravitationally lensed images of an extremely red object (ERO) at z =1.6, in the field of the massive cluster A 68 (z =0.255). We exploit the superlative resolution of our HST data and the enhanced spatial resolution and sensitivity afforded by the lens amplification to reconstruct the source-plane properties of this ERO. Our morphological and photometric analysis reveals that ERO J003707 is an L (star) early-type disc galaxy and we estimate that similar to10 per cent of galaxies with (R -K )greater than or equal to5.3 and K less than or equal to21 may have similar properties. The unique association of passive EROs with elliptical galaxies therefore appears to be too simplistic. We speculate on the evolution of ERO J003707: if gas continues to cool on to this galaxy in the manner predicted by hierarchical galaxy formation models, then by the present day, ERO J003707 could evolve into a very luminous spiral galaxy.