MusE GAs FLOw and Wind (MEGAFLOW) I: First MUSE results on background
  quasars
  The physical properties of galactic winds are one of the keys to understand
galaxy formation and evolution. These properties can be constrained thanks to
background quasar lines of sight (LOS) passing near star-forming galaxies
(SFGs). We present the first results of the MusE GAs FLOw and Wind (MEGAFLOW)
survey obtained of 2 quasar fields which have 8 MgII absorbers of which 3 have
rest-equivalent width greater than 0.8 \AA. With the new Multi Unit
Spectroscopic Explorer (MUSE) spectrograph on the Very Large Telescope (VLT),
we detect 6 (75$\%$) MgII host galaxy candidates withing a radius of 30 arcsec
from the quasar LOS. Out of these 6 galaxy--quasar pairs, from geometrical
arguments, one is likely probing galactic outflows, two are classified as
"ambiguous", two are likely probing extended gaseous disks and one pair seems
to be a merger. We focus on the wind$-$pair and constrain the outflow using a
high resolution quasar spectra from Ultraviolet and Visual Echelle Spectrograph
(UVES). Assuming the metal absorption to be due to gas flowing out of the
detected galaxy through a cone along the minor axis, we find outflow velocities
of the order of $\approx$ 150 km/s (i.e. smaller than the escape velocity) with
a loading factor, $\eta =\dot M_{\rm out}/$SFR, of $\approx$ 0.7. We see
evidence for an open conical flow, with a low-density inner core. In the
future, MUSE will provide us with about 80 multiple galaxy$-$quasar pairs in
two dozen fields.
