MusE GAs FLOw and Wind (MEGAFLOW) IV: A two sightline tomography of a
  galactic wind
  Galactic outflows are thought to eject baryons back out to the
circum-galactic medium (CGM). Studies based on metal absorption lines (MgII in
particular) in the spectra of background quasars indicate that the gas is
ejected anisotropically, with galactic winds likely leaving the host in a
bi-conical flow perpendicular to the galaxy disk. In this paper, we present a
detailed analysis of an outflow from a z = 0.7 "green-valley" galaxy
(log($M_*$/$\mathrm{M}_\odot$) = 9.9; SFR = 0.5
$\mathrm{M}_\odot\,\mathrm{yr}^{-1}$) probed by two background sources part of
the MUSE Gas Flow and Wind (MEGAFLOW) survey. Thanks to a fortuitous
configuration with a background quasar (SDSSJ1358+1145) and a bright background
galaxy at $z = 1.4$, both at impact parameters of $\approx 15\,\mathrm{kpc}$,
we can - for the first time - probe both the receding and approaching
components of a putative galactic outflow around a distant galaxy. We measure a
significant velocity shift between the MgII absorption from the two sightlines
($84\pm17\,\mathrm{km}\,\mathrm{s}^{-1}$), which is consistent with the
expectation from our simple fiducial wind model, possibly combined with an
extended disk contribution.
