K-luminous galaxies at z~2. Metallicity and B stars

We present the results from the analysis of the composite spectrum of five near-IR luminous (K < 20) galaxies at z~2. Several of the strongest absorption lines are present in the merging galaxy NGC 6090 UV spectrum and are not present in the spectra of Lyman Break Galaxies at z~3. They were identified as SiIII 1296, CIII 1428, SiII 1485, and Fe 1380 which are photospheric lines typical of B stars. A metallicity higher than solar is suggested by comparing the pure photospheric lines known as the 1425AA index (SiIII, CIII, FeV) with Starburst99 models. The evidence of high metallicity, together with the high masses, high star-formation rates, and possibly strong clustering, suggest that these galaxies are candidates to become massive spheroids.