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We present deep Keck/LRIS spectroscopy and HST/WFC3 imaging in the rest-frameoptical for a sample of eight galaxies at z~1.5 with highphotometrically-determined stellar masses. The data are combined withVLT/XShooter spectra of five galaxies from van de Sande et al. (2011, 2012 tobe submitted). We find that these thirteen galaxies have high velocitydispersions, with a median of sigma=301 km s^{-1}. This high value isconsistent with their relatively high stellar masses and compact sizes. Westudy their stellar populations using the strength of Balmer absorption lines,which are not sensitive to dust absorption. We find a large range in Balmerabsorption strength, with many galaxies showing very strong lines indicatingyoung ages. The median Hdelta_A equivalent width, determined directly orinferred from the H10 line, is 5.4 Angstroms, indicating a luminosity-weightedage of ~1 Gyr. Although this value may be biased towards higher values becauseof selection effects,high-dispersion galaxies with such young ages areextremely rare in the local Universe. Interestingly we do not find a simplecorrelation with rest-frame U-V color: some of the reddest galaxies have verystrong Balmer absorption lines. These results demonstrate that manyhigh-dispersion galaxies at z~1.5 were quenched recently. This implies thatthere must be a population of star-forming progenitors at z~2 with highvelocity dispersions or linewidths, which are notoriously absent from CO/Halphaselected surveys.

the astrophysical journal. letters

Massive and Newly Dead: Discovery of a Significant Population of  Galaxies with High Velocity Dispersions and Strong Balmer Lines at z~1.5 from  Deep Keck Spectra and HST/WFC3 Imaging