The SOAR Gravitational Arc Survey - I: Survey overview and photometric
  catalogs
  We present the first results of the SOAR (Southern Astrophysical Research)
Gravitational Arc Survey (SOGRAS). The survey imaged 47 clusters in two
redshift intervals centered at $z=0.27$ and $z=0.55$, targeting the richest
clusters in each interval. Images were obtained in the $g'$, $r'$ and $i'$
bands using the SOAR Optical Imager (SOI), with a median seeing of 0.83, 0.76
and 0.71 arcsec, respectively, in these filters. Most of the survey clusters
are located within the Sloan Digital Sky Survey (SDSS) Stripe 82 region and all
of them are in the SDSS footprint. Photometric calibration was therefore
performed using SDSS stars located in our SOI fields. We reached for galaxies
in all fields the detection limits of $g \sim 23.5$, $r \sim 23$ and $i \sim
22.5$ for a signal-to-noise ratio (S/N) = 3. As a by-product of the image
processing, we generated a source catalogue with 19760 entries, the vast
majority of which are galaxies, where we list their positions, magnitudes and
shape parameters. We compared our galaxy shape measurements to those of local
galaxies and concluded that they were not strongly affected by seeing. From the
catalogue data, we are able to identify a red sequence of galaxies in most
clusters in the lower $z$ range. We found 16 gravitational arc candidates
around 8 clusters in our sample. They tend to be bluer than the central
galaxies in the lensing cluster. A preliminary analysis indicates that $\sim
10%$ of the clusters have arcs around them, with a possible indication of a
larger efficiency associated to the high-$z$ systems when compared to the
low-$z$ ones. Deeper follow-up images with Gemini strengthen the case for the
strong lensing nature of the candidates found in this survey.
