The BOSS Emission-Line Lens Survey. IV. : Smooth Lens Models for the
  BELLS GALLERY Sample
  We present \textsl{Hubble Space Telescope} (\textsl{HST}) F606W-band imaging
observations of 21 galaxy-Ly$\alpha$ emitter lens candidates in the Baryon
Oscillation Spectroscopic Survey (BOSS) Emission-Line Lens Survey (BELLS) for
GALaxy-Ly$\alpha$ EmitteR sYstems (BELLS GALLERY) survey. 17 systems are
confirmed to be definite lenses with unambiguous evidence of multiple imaging.
The lenses are primarily massive early-type galaxies (ETGs) at redshifts of
approximately $0.55$, while the lensed sources are Ly$\alpha$ emitters (LAEs)
at redshifts from 2 to 3. Although the \textsl{HST} imaging data are well fit
by smooth lens models consisting of singular isothermal ellipsoids in an
external shear field, a thorough exploration of dark substructures in the lens
galaxies is required. The Einstein radii of the BELLS GALLERY lenses are on
average $60\%$ larger than those of the BELLS lenses because of the much higher
source redshifts which will allow a detailed investigation of the radius
evolution of the mass profile in ETGs. With the aid of the average $\sim 13
\times$ lensing magnification, the LAEs are resolved to comprise individual
star-forming knots of a wide range of properties with characteristic sizes from
less than 100 pc to several kpc, rest-frame far UV apparent AB magnitudes from
29.6 to 24.2, and typical projected separations of 500 pc to 2 kpc.
