The evolution of post starburst galaxies from z=2 to 0.5
We present the evolution in the number density and stellar mass functions of photometrically selected post starburst galaxies in the UKIDSSUltraDeep Survey,with redshifts of 0.5 10. We find that this transitionary species of galaxy is rare at all redshifts, contributing ~5 per cent of the total population at z 2, to <1 per cent by z 0.5. By comparing the mass functions of quiescent galaxies to post starburst galaxies at three cosmic epochs, we show that rapid quenching of star formation can account for 100 per cent of quiescent galaxy formation, if the post starburst spectral features are visible for ~250 Myr. The flattening of the low mass end of the quiescent galaxy stellar mass function seen at z 1 can be entirely explained by the addition of rapidly quenched galaxies. Only if a significant fraction of post starburst galaxies have features that are visible for longer than 250 Myr, or they acquire new gas and return to the star forming sequence, can there be significant growth of the red sequence from a slower quenching route. The shape of the mass function of these transitory post starburst galaxies resembles that of quiescent galaxies at z 2, with a preferred stellar mass of log (M/M) ~10.6, but evolves steadily to resemble that of star forming galaxies at z 2 they are exclusively massive galaxies that have formed the bulk of their stars during a rapid assembly period, followed by complete quenching of further star formation; (2) at z