Kinematics of the SN Refsdal host revealed by MUSE: a regularly rotating
  spiral galaxy at z~1.5
  We use Multi Unit Spectroscopic Explorer (MUSE) observations of the galaxy
cluster MACS J1149.5+2223 to explore the kinematics of the grand-design spiral
galaxy Sp1149 hosting the SN Refsdal. Sp1149 lies at $z\simeq1.49$, has a
stellar mass $M_*\simeq5\times10^9 \, \mathrm{M_\odot}$, a star-formation rate
$\mathrm{SFR} \simeq1-6 \, \mathrm{M_\odot/yr}$ and represents a likely
progenitor of a Milky-Way-like galaxy. All the four multiple images of Sp1149
in our data show strong OII-line emissions pointing to a clear rotation
pattern. We take advantage of the gravitational lensing magnification effect
($\simeq 4 \times$) on the OII emission of the least distorted image to fit 3D
kinematic models to the MUSE data-cube and derive the rotation curve and the
velocity dispersion profile of Sp1149. We find that the rotation curve steeply
rises, peaks at $R\simeq1$ kpc and then (initially) declines and flattens to an
average $V_\mathrm{flat} = 128^{+29}_{-19}$ km/s. The shape of the rotation
curve is well determined but the actual value of $V_\mathrm{flat}$ is quite
uncertain because of the nearly face-on configuration of the galaxy. The
intrinsic velocity dispersion due to gas turbulence is almost constant across
the entire disc with an average of $27\pm5$ km/s. This value is consistent with
$z=0$ measurements in the ionized gas component and a factor 2-4 lower than
other estimates in different galaxies at similar redshifts. The average
stellar-to-total mass fraction is of the order of one fifth. Our kinematic
analysis returns the picture of a regular star-forming, mildly turbulent,
rotation-dominated ($V / \sigma\simeq5$) spiral galaxy in a 4 Gyr old Universe.
