  We report the discovery of six spatially extended (10-100 kpc) line-emitting
nebulae in the z=0.57 galaxy group hosting PKS0405-123, one of the most
luminous quasars at z<1. The discovery is enabled by the Multi Unit
Spectroscopic Explorer (MUSE) and provides tantalizing evidence connecting
large-scale gas streams with nuclear activity on scales of <10 proper kpc
(pkpc). One of the nebulae exhibits a narrow, filamentary morphology extending
over 50 pkpc toward the quasar with narrow internal velocity dispersion (50
km/s) and is not associated with any detected galaxies, consistent with a cool
intragroup medium (IGrM) filament. Two of the nebulae are 10 pkpc North and
South of the quasar with tidal arm like morphologies. These two nebulae, along
with a continuum emitting arm extending 60 pkpc from the quasar are signatures
of interactions which are expected to redistribute angular momentum in the host
interstellar medium (ISM) to facilitate star formation and quasar fueling in
the nucleus. The three remaining nebulae are among the largest and most
luminous [O III] emitting `blobs' known (1400-2400 pkpc^2) and correspond both
kinematically and morphologically with interacting galaxy pairs in the quasar
host group, consistent with arising from stripped ISM rather than large-scale
quasar outflows. The presence of these large- and small-scale nebulae in the
vicinity of a luminous quasar bears significantly on the effect of large-scale
environment on galaxy and black hole fueling, providing a natural explanation
for the previously known correlation between quasar luminosity and cool
circumgalactic medium (CGM).
