A Near‐Infrared Spectroscopic Survey ofK‐Selected Galaxies atz∼ 2.3: Redshifts and Implications for Broadband Photometric Studies

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Abstract
Using the Gemini Near-Infrared Spectrograph (GNIRS), we have completed a near-infrared spectroscopic survey for K-bright galaxies at z ~ 2.3 selected from the MUSYC survey. We derived spectroscopic redshifts from emission lines or from continuum features and shapes for all 36 observed galaxies. The continuum redshifts are driven by the Balmer/4000 Å break and have an uncertainty in Δ z/(1 + z) of z/(1 + z) . The systematic error can be reduced by using optimal templates and deep photometry; the random error, however, will be hard to reduce below 5%. The spectra lead to significantly improved constraints for stellar population parameters. For most quantities this improvement is about equally driven by the higher spectral resolution and by the much reduced redshift uncertainty. Properties such as the age, AV, current star formation rate, and the star formation history are generally very poorly constrained with broadband data alone. Interestingly, stellar masses and mass-to-light ratios are among the most stable parameters from broadband data. Nevertheless, photometric studies may overestimate the number of massive galaxies at 2 < z < 3 and thus underestimate the evolution of the stellar mass density. Finally, the spectroscopy supports our previous finding that red galaxies dominate the high-mass end of the galaxy population at z = 2-3.
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