  In order to investigate the effects of galaxy mergers throughout the
interaction sequence, we present a study of 10,800 galaxies in close pairs and
a smaller sample of 97 post-mergers identified in the Sloan Digital Sky Survey.
We find that the average central star formation rate (SFR) enhancement (x 3.5)
and the fraction of starbursts (20 per cent) peak in the post-merger sample.
The post-mergers also show a stronger deficit in gas phase metallicity than the
closest pairs, being more metal-poor than their control by -0.09 dex. Combined
with the observed trends in SFR and the timescales predicted in merger
simulations, we estimate that the post-mergers in our sample have undergone
coalescence within the last few hundred Myr. In contrast with the incidence of
star-forming galaxies, the frequency of active galactic nuclei (AGN) peaks in
the post-mergers, outnumbering AGN in the control sample by a factor of 3.75.
Moreover, amongst the galaxies that host an AGN, the black hole accretion rates
in the closest pairs and post-mergers are higher by a factor of ~3 than AGN in
the control sample. These results are consistent with a picture in which star
formation is initiated early on in the encounter, with AGN activity peaking
post-coalescence.
