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We present first results of a spectroscopic survey targeting K-selectedgalaxies at z=2.0-2.7 using the GNIRS instrument on Gemini-South. We obtainednear-infrared spectra with a wavelength coverage of 1.0-2.5 micron for 26K-bright galaxies (K<19.7) selected from the MUSYC survey using photometricredshifts. We successfully derived spectroscopic redshifts for all 26 galaxiesusing rest-frame optical emission lines or the redshifted Balmer/4000 Angstrombreak. Twenty galaxies have spectroscopic redshifts in the range 2.0<z<2.7, forwhich bright emission lines like Halpha and [OIII] fall in atmospheric windows.Surprisingly, we detected no emission lines for nine of these 20 galaxies. Themedian 2 sigma upper limit on the rest-frame equivalent width of Halpha forthese nine galaxies is ~10 Angstrom. The stellar continuum emission of thesesame nine galaxies is best fitted by evolved stellar population models. Thebest-fit star formation rate (SFR) is zero for five out of nine galaxies, andconsistent with zero within 1 sigma for the remaining four. Thus, both theHalpha measurements and the independent stellar continuum modeling imply that45% of our K-selected galaxies are not forming stars intensely. This highfraction of galaxies without detected line emission and low SFRs may imply thatthe suppression of star formation in massive galaxies occurs at higher redshiftthan is predicted by current CDM galaxy formation models. However, obscuredstar formation may have been missed, and deep mid-infrared imaging is needed toclarify this situation.Comment: Accepted for publication in ApJ Letter

Spectroscopic Identification of Massive Galaxies at z ~ 2.3 with Strongly Suppressed Star Formation