Jellyfish: Resolving the Kinematics of Extreme Ram-pressure Stripping at z ∼ 0.3

We present and discuss results from the first spatially resolved kinematic study of ram-pressure stripping of a massive late-type galaxy at intermediate redshifts. Our target, the spectacular “jellyfish” galaxy, A1758N_JFG1, was previously identified as a fast-moving member of the equal-mass merger A1758N ( z = 0.28), with a star formation rate of 48 M ☉ yr −1 , far above the galaxy main sequence. Integral field unit (IFU) data obtained by us unambiguously confirm ram-pressure stripping as the physical mechanism driving the optical morphology and high star formation rate of this system by revealing extended [O ii ] λ 3727 Å emission up to 40 kpc (in projection) downstream, as well as an ordered radial-velocity field generated by (a) conservation of angular momentum of the interstellar gas stripped from the edge of the galactic disk and (b) drag forces exerted by the intracluster medium on the “tentacles” of stripped material. We find no evidence of significant nuclear activity in A1758N_JFG1, although an AGN might, at this early stage of the stripping process, be obscured by high column densities of gas and dust near the galactic core. Finally, our exploration of possible trajectories of A1758N_JFG1 found solutions consistent with the notions (a) that the A1758N merger proceeds along an axis that is substantially inclined with respect to the plane of the sky and (b) that A1758N_JFG1 participated in the merger, rather than having been accreted independently from the field.