The evolution of galaxies from primeval irregulars to present-day ellipticals

Galaxy formation is believed to proceed in a 'bottom up' manner, starting with the formation of small clumps of gas and stars that then merge hierarchically into giant systems(1,2). The baryonic gas loses thermal energy by radiative cooling and falls towards the centres of the new galaxies, while supernovae blow gas out(3,4). Any realistic model therefore requires a proper treatment of these processes, but hitherto this has been far from satisfactory(5). Here we report a simulation that follows evolution from the earliest stages of galaxy formation through the period of dynamical relaxation, at which point the resulting galaxy is in its final form. The bubble structures of gas revealed in our simulation (for times of less than 3 x 10(8) years) resemble closely high-red-shift Lyman-alpha emitters(6,7). After 10(9) years, these bodies are dominated by stellar continuum radiation and then resemble the Lyman break galaxies(8,9), which are high-redshift star-forming galaxies. At this point, the abundance of elements heavier than helium ('metallicity') appears to be solar. After 1.3 x 10(10) years, these galaxies resemble present-day ellipticals.