Discovery of a Population of Evolved and Massive Galaxies at High Redshift

We present a new technique for identifying massive and evolved galaxies at z∼5. The technique is based on broad-band deep photometry, using the strength of Balmer Break features, which is shifted between the K-band and m 3.6 wavelengths at this redshift. The main criterion we use to identify these galaxies is therefore the K–m 3.6 colors. We found a total of 11 galaxies in the GOODS-S field at z∼5, with stellar masses between 1010 and 5×1011 M⊙ and ages >100 Myr. The existence of such a population of galaxies strongly constrains current galaxy formation scenarios. The implications of this population for formation of galaxies is discussed.