2016ApJ...819...74H

Measuring stellar velocity dispersions of quiescent galaxies beyond z∼2 is observationally challenging. Such measurements require near-infrared spectra with a continuum detection of at least moderate signal to noise, often necessitating long integrations. In this paper, we present deep X-Shooter spectroscopy of one of only two known gravitationally lensed massive quiescent galaxies at z> 2. This galaxy is quadruply imaged, with the brightest images magnified by a factor of ∼5. The total exposure time of our data is 9.8 hr on-source; however, the magnification, and the slit placement encompassing two images, provides a total equivalent exposure time of 215 hr. From this deep spectrum we measure a redshift of (z_spec=2.756±0.001), making this one of the highest redshift quiescent galaxies that is spectroscopically confirmed. We simultaneously fit both the spectroscopic and photometric data to determine stellar population parameters and conclude that this galaxy is relatively young (560_–80⁺¹⁰⁰ Myr), of intermediate mass (log M_*/M_☉=10.59_–0.05^+0.04), consistent with low dust content (A_V=0.20_–0.20^+0.26), and has quenched only relatively recently. This recent quenching is confirmed by strong Balmer absorption, particularly Hδ(Hδ_A=6.66_–0.92^+0.96). Remarkably, this proves that at least some intermediate-mass galaxies have already quenched as early as z∼2.8. Additionally, we have measured a velocity dispersion of (σ =187±43 km s^–1), making this the highest-redshift quiescent galaxy with a dispersion measurement. We confirm that this galaxy falls on the same mass fundamental plane (MFP) as galaxies at z = 2.2, consistent with little to no evolution in the MFP up to z = 2.8. Overall this galaxy is proof of the existence of intermediate-mass quenched galaxies in the distant universe, and that lensing is a powerful tool for determining their properties with improved accuracy.