The evolution of post-starburst galaxies from z=2 to 0.5

• Published in: Monthly notices of the Royal Astronomical Society Vol. 463; no. 1; pp. 832 - 844
• Main Authors: Wild, Vivienne, Almaini, Omar, Dunlop, Jim, Simpson, Chris, Rowlands, Kate, Bowler, Rebecca, Maltby, David, McLure, Ross
• Format: Journal Article
• Language: English
• Published: London Oxford University Press 21-11-2016
• Subjects: Galactic evolution; Galaxies; Galaxy formation; Quenching; Rapid quenching (metallurgy); Red shift; Space telescopes; Star & galaxy formation; Star formation; Starbursts; Stellar mass; galaxies: formation; galaxies: luminosity function, mass function; galaxies: evolution; galaxies: high-redshift; galaxies: stellar content
• ISSN: 0035-8711; 1365-2966
• DOI: 10.1093/mnras/stw1996

We present the evolution in the number density and stellar mass functions of photometrically selected post-starburst galaxies in the UKIDSS Ultra Deep Survey, with redshifts of 0.5 < z < 2 and stellar masses log (M/M⊙) >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 < 1. This leads us to propose a dual origin for post-starburst galaxies: (1) 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 ≲ 1 they are caused by the rapid quenching of gas-rich star-forming galaxies, independent of stellar mass, possibly due to environment and/or gas-rich major mergers.