Averaged spectrum of old galaxies

Averaged spectrum (blue) of four old massive galaxies compared to a set of template spectra. The bottom compares it with the spectrum of a star having a surface temperature of 7200 degrees (green) and 6800 degrees (red), respectively. The upper graph makes a comparison with synthetic spectra of simulated simple stellar populations with ages of 500, 1,100 and 3,000 million years. This figure demonstrates that the newly found galaxies mostly contain old low-mass stars and must have formed between 1,000 and 2,000 million years earlier than the epoch at which they are now seen.