Spatially Resolved Stellar Kinematics from LEGA-C: Increased Rotational Support in z ∼ 0.8 Quiescent Galaxies

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 10-20kpc, or to an average of 2.7R e . Combined with central stellar velocity dispersions (σ 0 ) 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 × 10 11 M ) generally show no or little rotation measured at 5kpc (|V 5 |/σ 0 < 0.2 in 8 of 10 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 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 5kpc 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.

Stellar Kinematics and Environment at z ∼ 0.8 in the LEGA-C Survey: Massive Slow Rotators Are Built First in Overdense Environments

“…In the two right-most panels, we show the running average rotational support for each overdensity bin, with a slight offset from the center of the bin for clarity. As shown in Bezanson et al (2018b), the average range in rotational support tends to decrease with increasing stellar mass, which is consistent with studies of massive, quiescent galaxies in the local Universe (Veale et al 2017;Greene et al 2018). We do not see a strong environmental trend at all masses, but we note two statistically significant trends at the massive end of the sample.…”

First results from the TNG50 simulation: the evolution of stellar and gaseous discs across cosmic time

“…It will be possible to explicitly search for and test these expectations at intermediate and high redshifts using future observations with the James Webb Telescope (JWST) and Extremely Large Telescope (ELT). In fact, the LEGA-C survey (van der Wel et al 2016) is providing the first systematic exploration of stellar dynamical structure of intermediate-redshift galaxies (z 1, Bezanson et al 2018) and the first results on star-forming galaxies are forthcoming.…”

Rejuvenation in z ∼ 0.8 Quiescent Galaxies in LEGA-C

“…Emission line spectra are computed using the Penalized Pixel-Fitting method (pPXF, Cappellari & Emsellem 2004). For details of the emission line fitting procedure, see Bezanson et al (2018). The model results in measurements of stellar masses (M * ,spec ), luminosities (L spec ), mean massweighted and light-weighted ages (a <M W > and a <LW > , respectively) and the dust reddening values.…”