Spectroscopic Confirmation of a Substantial Population of Luminous Red Galaxies at Redshifts z ≳ 2

We confirm spectroscopically the existence of a population of galaxies at z ≳ 2 with rest-frame optical colors similar to normal nearby galaxies. The galaxies were identified by their red near-infrared colors in deep images obtained with the Infrared Spectrometer and Array Camera on the Very Large Telescope of the field around the foreground cluster MS 1054-03. Redshifts of six galaxies with Js-Ks > 2.3 were measured from optical spectra obtained with the W. M. Keck telescope. Five out of six are in the range 2.43 ≤ z ≤ 3.52, demonstrating that the Js-Ks color selection is quite efficient. The rest-frame ultraviolet spectra of confirmed z > 2 galaxies display a range of properties, with two galaxies showing emission lines characteristic of active galactic nuclei, two having Lyα in emission, and one showing interstellar absorption lines only. Their full spectral energy distributions are well described by constant star formation models with ages 1.4-2.6 Gyr, except for one galaxy whose colors indicate a dusty starburst. The confirmed z > 2 galaxies are very luminous: their Ks magnitudes are in the range 19.2-19.9, corresponding to rest-frame absolute V magnitudes from -24.8 to -23.2. Assuming that our bright spectroscopic sample is representative for the general population of Js-Ks selected objects, we find that the surface density of red z ≳ 2 galaxies is ≈0.9 arcmin-2 to Ks = 21. The surface density is comparable to that of Lyman break-selected galaxies with Ks < 21, when corrections are made for the different redshift distributions of the two samples. Although there will be some overlap between the two populations, most "optical-break" galaxies are too faint in the rest-frame ultraviolet to be selected as Lyman break galaxies. The most straightforward interpretation is that star formation in typical optical-break galaxies started earlier than in typical Lyman break galaxies. Optical-break galaxies may be the oldest and most massive galaxies yet identified at z > 2, and they could evolve into early-type galaxies and bulges.