Spatially Resolved Stellar Kinematics from LEGA-C: Increased Rotational Support in z ∼ 0.8 Quiescent Galaxies
Bell, Eric F.; Maseda, Michael V.; Franx, Marijn; Muzzin, Adam; Labbé, Ivo; van Dokkum, Pieter; van der Wel, Arjen; van Houdt, Josha; Bezanson, Rachel; Pacifici, Camilla; Gallazzi, Anna; Sobral, David; Brammer, Gabriel B.; van de Sande, Jesse; Wu, Po-Feng; Noeske, Kai; Barišić, Ivana; Straatman, Caroline; Chauke, Priscilla; Calhau, Joao; Muños-Mateos, Juan Carlos
United States, Belgium, Germany, United Kingdom, Netherlands, Italy, Chile, Canada, Australia
Abstract
We present stellar rotation curves and velocity dispersion profiles for 104 quiescent galaxies at z = 0.6-1 from the Large Early Galaxy Astrophysics Census (LEGA-C) spectroscopic survey. Rotation is typically probed across 10-20 kpc, or to an average of 2.7Re. Combined with central stellar velocity dispersions (σ0) this provides the first determination of the dynamical state of a sample selected by a lack of star formation activity at large lookback time. The most massive galaxies (M⋆ > 2 × 1011 M⊙) generally show no or little rotation measured at 5 kpc (| {V}5| /{σ }0< 0.2 in eight of ten cases), while ∼64% of less massive galaxies show significant rotation. This is reminiscent of local fast- and slow-rotating ellipticals and implies that low- and high-redshift quiescent galaxies have qualitatively similar dynamical structures. We compare | {V}5| /{σ }0 distributions at z ∼ 0.8 and the present day by re-binning and smoothing the kinematic maps of 91 low-redshift quiescent galaxies from the Calar Alto Legacy Integral Field Area (CALIFA) survey and find evidence for a decrease in rotational support since z ∼ 1. This result is especially strong when galaxies are compared at fixed velocity dispersion; if velocity dispersion does not evolve for individual galaxies then the rotational velocity at 5 kpc was an average of 94 ± 22% higher in z ∼ 0.8 quiescent galaxies than today. Considering that the number of quiescent galaxies grows with time and that new additions to the population descend from rotationally supported star-forming galaxies, our results imply that quiescent galaxies must lose angular momentum between z ∼ 1 and the present, presumably through dissipationless merging, and/or that the mechanism that transforms star-forming galaxies also reduces their rotational support.