The relationship between gas and galaxies at z<1 using the Q0107 quasar
  triplet
  We study the distribution and dynamics of the circum- and intergalactic
medium using a dense galaxy survey covering the field around the Q0107 system,
a unique z~1 projected quasar triplet. With full Ly$\alpha$ coverage along all
three lines-of-sight from z=0.18 to z=0.73, more than 1200 galaxy spectra, and
two MUSE fields, we examine the structure of the gas around galaxies on
100-1000 kpc scales. We search for H I absorption systems occurring at the same
redshift (within 500 $\textrm{km}$ $\textrm{s}^{-1}$) in multiple sightlines,
finding with $>$ 99.9% significance that these systems are more frequent in the
observed quasar spectra than in a randomly distributed population of absorbers.
This is driven primarily by absorption with column densities N(H I) $> 10^{14}$
$\textrm{cm}^{-2}$, whilst multi-sightline absorbers with lower column
densities are consistent with a random distribution. Star-forming galaxies are
more likely to be associated with multi-sightline absorption than quiescent
galaxies. HST imaging provides inclinations and position angles for a subset of
these galaxies. We observe a bimodality in the position angle of detected
galaxy-absorber pairs, again driven mostly by high-column-density absorbers,
with absorption preferentially along the major and minor axes of galaxies out
to impact parameters of several hundred kpc. We find some evidence supporting a
disk/outflow dichotomy, as H I absorbers near the projected major-axis of a
galaxy show line-of-sight velocities that tend to align with the rotation of
that galaxy, whilst minor-axis absorbers are twice as likely to exhibit O VI at
the same redshift.
