The BOSS Emission-Line Lens Survey (BELLS). I. A large spectroscopically
  selected sample of Lens Galaxies at redshift ~ 0.5
  We present a catalog of 25 definite and 11 probable strong galaxy-galaxy
gravitational lens systems with redshifts 0.4 \lesssim z \lesssim 0.7,
discovered spectroscopically by the presence of higher redshift emission-lines
within the Baryon Oscillation Spectroscopic Survey (BOSS) of luminous galaxies,
and confirmed with high-resolution Hubble Space Telescope (HST) images of 44
candidates. Our survey extends the methodology of the Sloan Lens ACS Survey
(SLACS: Bolton et al. 2006; 2008) to higher redshift. We describe the details
of the BOSS spectroscopic candidate detections, our HST Adanced Camera for
Surveys (ACS) image processing and analysis methods, and our strong
gravitational lens modeling procedure. We report BOSS spectroscopic parameters
and ACS photometric parameters for all candidates, and mass-distribution
parameters for the best-fit singular isothermal ellipsoid models of definite
lenses. Our sample to date was selected using only the first six months of BOSS
survey-quality spectroscopic data. The full 5-year BOSS database should produce
a sample of several hundred strong galaxy-galaxy lenses and in combination with
SLACS lenses at lower redshift, strongly constrain the redshift evolution of
the structure of elliptical, bulge-dominated galaxies as a function of
luminosity, stellar mass, and rest-frame color, thereby providing a powerful
test for competing theories of galaxy formation and evolution.
