Evidence for solar metallicities in massive star-forming galaxies at z≳2

We present results of near-IR spectroscopic measurements of seven star-forming galaxies at 2.1 < z < 2.5. Drawn from a large spectroscopic survey of galaxies photometrically preselected by their U(n)GR colors to lie at z similar to 2, these galaxies were chosen for their bright rest-frame optical luminosities (K-s less than or equal to 20.0). Most strikingly, the majority of the sample of seven galaxies exhibit [N II]/ Halpha nebular emission-line ratios indicative of at least solar H II region metallicities, at a look-back time of 10.5 Gyr. The broadband colors of the K-s-bright sample indicate that most have been forming stars for more than a gigayear at z similar to 2 and have already formed stellar masses in excess of 10(11) M-.. The descendants of these galaxies in the local universe are most likely metal-rich and massive spiral and elliptical galaxies, while plausible progenitors for them can be found among the population of z similar to 3 Lyman break galaxies. While the K-s-bright z similar to 2 galaxies appear to be highly evolved systems, their large Halpha luminosities and uncorrected Halpha star formation rates of 24 - 60 M-. yr(-1) indicate that active star formation is still ongoing. The luminous UV-selected objects presented here comprise more than half of the high-redshift (z > 1.5) tails of current K-band - selected samples such as the K20 and Gemini Deep Deep surveys.