The Strong Gravitationally Lensed Herschel Galaxy HLock01: Optical
  Spectroscopy Reveals a Close Galaxy Merger with Evidence of Inflowing Gas
  The submillimeter galaxy (SMG) HERMES J105751.1+573027 (hereafter HLock01) at
z = 2.9574 +/- 0.0001 is one of the brightest gravitationally lensed sources
discovered in the Herschel Multi-tiered Extragalactic Survey. Apart from the
high flux densities in the far-infrared, it is also extremely bright in the
rest-frame ultraviolet (UV), with a total apparent magnitude m_UV = 19.7 mag.
We report here deep spectroscopic observations with the Gran Telescopio
Canarias of the optically bright lensed images of HLock01. Our results suggest
that HLock01 is a merger system composed of the Herschel-selected SMG and an
optically bright Lyman break-like galaxy (LBG), separated by only 3.3 kpc in
projection. While the SMG appears very massive (M* = 5x10^11 Msun), with a
highly extinguished stellar component (A_V = 4.3), the LBG is a young,
lower-mass (M* = 1x10^10 Msun), but still luminous (10xL*_UV) satellite galaxy.
Detailed analysis of the high signal-to-noise (S/N) rest-frame UV spectrum of
the LBG shows complex kinematics of the gas, exhibiting both blueshifted and
redshifted absorption components. While the blueshifted component is associated
with strong galactic outflows from the massive stars in the LBG, as is common
in most star-forming galaxies, the redshifted component may be associated with
gas inflow seen along a favorable sightline to the LBG. We also find evidence
of an extended gas reservoir around HLock01 at an impact parameter of 110 kpc,
through the detection of C II 1334$\AA$ absorption in the red wing of a bright
Ly-alpha emitter at z = 3.327. The data presented here highlight the power of
gravitational lensing in high S/N studies to probe deeply into the physics of
high-z star forming galaxies.
