Discovery of a Strongly Lensed Massive Quiescent Galaxy at z = 2.636: Spatially Resolved Spectroscopy and Indications of Rotation

Abstract

We report the discovery of RG1M0150, a massive, recently quenched galaxy at z = 2.636 that is multiply imaged by the cluster MACSJ0150.3-1005. We derive a stellar mass of log M_* = 11.49_(-0.16)^(+0.10) and a half-light radius of R_(e,maj) = 1.8 ± 0.4 kpc. Taking advantage of the lensing magnification, we are able to spatially resolve a remarkably massive yet compact quiescent galaxy at z > 2 in ground-based near-infrared spectroscopic observations using Magellan/FIRE and Keck/MOSFIRE. We find no gradient in the strength of the Balmer absorption lines over 0.6R_e - 1.6R_e, which are consistent with an age of 760 Myr. Gas emission in [N ii] broadly traces the spatial distribution of the stars and is coupled with weak Hα emission (log [N ii]/Hɑ = 0.6 ± 0.2, indicating that OB stars are not the primary ionizing source. The velocity dispersion within the effective radius is σ_(e,stars) = 271 ± 41 km s^(-1). We detect rotation in the stellar absorption lines for the first time beyond z ~ 1. Using a two-integral Jeans model that accounts for observational effects, we measure a dynamical mass of log M_(dyn) = 11.24 ± 0.14 and V/σ = 0.70 ± 0.21. This is a high degree of rotation considering the modest observed ellipticity of 0.12 ± 0.08, but it is consistent with predictions from dissipational merger simulations that produce compact remnants. The mass of RG1M0150 implies that it is likely to become a slowly rotating elliptical. If it is typical, this suggests that the progenitors of massive ellipticals retain significant net angular momentum after quenching which later declines, perhaps through accretion of satellites.

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