2004ApJ...614L...9M

We present spectroscopic evidence from the Gemini Deep Deep Survey for a significant population of color-selected red galaxies at 1.3<z<2.2 whose integrated light is dominated by evolved stars. Unlike radio-selected objects, the z>1.5 old galaxies have a sky density greater than 0.1/arcmin2. Conservative age estimates for 20 galaxies with z>1.3, <z≥1.49, give a median age of 1.2 Gyr and <z_f≥2.4. One-quarter of the galaxies have inferred z_f>4. Models restricted to [Fe/H]≤0 give median ages and z_fof 2.3 Gyr and 3.3, respectively. These galaxies are among the most massive and contribute ∼50% of the stellar mass density at 1<z<2. The derived ages and most probable star formation histories suggest a high star formation rate (∼300-500 M_☉/yr) phase in the progenitor population. We argue that most of the red galaxies are not descendants of the typical z∼3 Lyman break galaxies. Galaxies associated with luminous submillimeter sources have the requisite star formation rates to be the progenitor population. Our results point toward early and rapid formation for a significant fraction of present-day massive galaxies.