Reionization and high-redshift galaxies: the view from quasar absorption
  lines
  Determining when and how the first galaxies reionized the intergalactic
medium (IGM) promises to shed light on both the nature of the first objects and
the cosmic history of baryons. Towards this goal, quasar absorption lines play
a unique role by probing the properties of diffuse gas on galactic and
intergalactic scales. In this review we examine the multiple ways in which
absorption lines trace the connection between galaxies and the IGM near the
reionization epoch. We first describe how the Ly$\alpha$ forest is used to
determine the intensity of the ionizing ultraviolet background and the global
ionizing emissivity budget. Critically, these measurements reflect the escaping
ionizing radiation from all galaxies, including those too faint to detect
directly. We then discuss insights from metal absorption lines into
reionization-era galaxies and their surroundings. Current observations suggest
a buildup of metals in the circumgalactic environments of galaxies over $z \sim
6$ to 5, although changes in ionization will also affect the evolution of metal
line properties. A substantial fraction of metal absorbers at these redshifts
may trace relatively low-mass galaxies. Finally, we review constraints from the
Ly$\alpha$ forest and quasar near zones on the timing of reionization. Along
with other probes of the high-redshift Universe, absorption line data are
consistent with a relatively late end to reionization ($5.5 \lesssim z \lesssim
7$); however the constraints are still fairly weak. Significant progress is
expected to come through improved analysis techniques, increases in the number
of known high-redshift quasars from optical and infrared sky surveys, large
gains in sensitivity from next-generation observing facilities, and synergies
with other probes of the reionization era.
