MUSE Analysis of Gas around Galaxies (MAGG) -- I: Survey design and the
  environment of a near pristine gas cloud at z~3.5
  We present the design, methods, and first results of the MUSE Analysis of Gas
around Galaxies (MAGG) survey, a large programme on the Multi Unit
Spectroscopic Explorer (MUSE) instrument at the Very Large Telescope (VLT)
which targets 28 z > 3.2 quasars to investigate the connection between
optically-thick gas and galaxies at z~3-4. MAGG maps the environment of 52
strong absorption line systems at z > 3, providing the first statistical sample
of galaxies associated with gas-rich structures in the early Universe. In this
paper, we study the galaxy population around a very metal poor gas cloud at
z~3.5 towards the quasar J124957.23-015928.8. We detect three Lyman alpha
emitters within <200km/s of the cloud redshift, at projected separations <185
kpc (physical). The presence of star-forming galaxies near a very metal-poor
cloud indicates that metal enrichment is still spatially inhomogeneous at this
redshift. Based on its very low metallicity and the presence of nearby
galaxies, we propose that the most likely scenario for this LLS is that it lies
within a filament which may be accreting onto a nearby galaxy. Taken together
with the small number of other LLSs studied with MUSE, the observations to date
show a range of different environments near strong absorption systems. The full
MAGG survey will significantly expand this sample and enable a statistical
analysis of the link between gas and galaxies to pin down the origin of these
diverse environments at z~3-4.
