Fast rotators at cosmic noon: Stellar kinematics for 15 quiescent galaxies from JWST-SUSPENSE

We present spatially resolved stellar kinematics of 15 massive (M* = 1010.5 − 11.5 M⊙) quiescent galaxies at z ∼ 1.2 − 2.3 from the JWST-SUSPENSE program. This is the largest sample of spatially resolved kinematic measurements of quiescent galaxies at cosmic noon to date. Our measurements are derived from ultra-deep NIRSpec/MSA stellar absorption line spectra using a forward-modelling approach that accounts for optics, source morphology, positioning, and data reduction effects. Ten out of 15 galaxies are orientated such that we can measure rotational support. Remarkably, all 10 galaxies show significant rotation (Vre = 117 − 345 km s−1, σ0 = 180 − 387 km s−1) and are classified as fast rotators from their spin parameter. The remaining galaxies are too misaligned with respect to the slitlet to constrain their rotational velocities. The widespread rotational support in our sample indicates that the process responsible for quenching star formation in early massive galaxies did not destroy rotating disc structures. When combined with other quiescent galaxy samples at z ∼ 0.5 − 2.5, we find a trend between rotational support and age, where younger quiescent galaxies are more rotationally supported. This age trend was also found at z ∼ 0, and it likely explains why our high-redshift galaxies have more rotational support than massive early-type galaxies at z ∼ 0, which are older on average. Our kinematic modelling also enabled us to calculate dynamical masses. These dynamical masses greatly exceed the stellar masses for our sample (median Mdyn/M* = 2.73); they even allow for the bottom-heavy initial mass function found in the cores of low-z massive ellipticals. Altogether, our results support a scenario in which distant quiescent galaxies evolve into nearby massive early-type galaxies, by gradually building up their outskirts, and simultaneously losing rotation through a series of (mostly minor) mergers.