2018MNRAS.476..804D

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 supernova 'Refsdal'. Sp1149 lies at z ≃ 1.49, has a stellar mass M_* ≃ 5 x 10⁹ M_☉, has a star formation rate (SFR) ≃1-6 M_☉ yr^–1, and represents a likely progenitor of a Milky Way-like galaxy. All the four multiple images of Sp1149 in our data show strong [O II]-line emissions pointing to a clear rotation pattern. We take advantage of the gravitational lensing magnification effect (≃4x) on the [O II] emission of the least distorted image to fit three-dimensional 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 ≃ 1 kpc, and then (initially) declines and flattens to an average V_flat= 128⁺²⁹_–19 km s^–1. The shape of the rotation curve is well determined, but the actual value of V_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 ± 5 km s^–1. This value is consistent with z = 0 measurements in the ionized gas component and a factor of 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/σ ≃ 5) spiral galaxy in a 4-Gyr-old Universe.