The serendipitous observation of a gravitationally lensed galaxy at z =
  0.9057 from the Blanco Cosmology Survey: The Elliot Arc
  We report on the serendipitous discovery in the Blanco Cosmology Survey (BCS)
imaging data of a z = 0.9057 galaxy that is being strongly lensed by a massive
galaxy cluster at a redshift of z=0.3838. The lens (BCS J2352-5452) was
discovered while examining i- and z-band images being acquired in October 2006
during a BCS observing run. Follow-up spectroscopic observations with the GMOS
instrument on the Gemini South 8m telescope confirmed the lensing nature of
this system. Using weak plus strong lensing, velocity dispersion, cluster
richness N_200, and fitting to an NFW cluster mass density profile, we have
made three independent estimates of the mass M_200 which are all very
consistent with each other. The combination of the results from the three
methods gives M_200 = (5.1 +- 1.3) x 10^14 M_Sun, which is fully consistent
with the individual measurements. The final NFW concentration c_200 from the
combined fit is c_200 = 5.4(+1.4 -1.1). We have compared our measurements of
M_200 and c_200 with predictions for (a) clusters from Lambda_CDM simulations,
(b) lensing selected clusters from simulations, and (c) a real sample of
cluster lenses. We find that we are most compatible with the predictions for
Lambda_CDM simulations for lensing clusters, and we see no evidence based on
this one system for an increased concentration compared to Lambda_CDM. Finally,
using the flux measured from the [OII]3727 line we have determined the star
formation rate (SFR) of the source galaxy and find it to be rather modest given
the assumed lens magnification.
