We use the eagle simulations to study the connection between the quenching timescale, τ Q , and the physical mechanisms that transform star-forming galaxies into passive galaxies. By quantifying τ Q in two complementary ways -as the time over which (i) galaxies traverse the green valley on the colour-mass diagram, or (ii) leave the main sequence of star formation and subsequently arrive on the passive cloud in specific star formation rate (SSFR)-mass space -we find that the τ Q distribution of high-mass centrals, low-mass centrals and satellites are divergent. In the low stellar mass regime where M < 10 9.6 M , centrals exhibit systematically longer quenching timescales than satellites (≈ 4 Gyr compared to ≈ 2 Gyr). Satellites with low stellar mass relative to their halo mass cause this disparity, with ram pressure stripping quenching these galaxies rapidly. Low mass centrals are quenched as a result of stellar feedback, associated with long τ Q 3 Gyr. At intermediate stellar masses where 10 9.7 M < M < 10 10.3 M , τ Q are the longest for both centrals and satellites, particularly for galaxies with higher gas fractions. At M 10 10.3 M , galaxy merger counts and black hole activity increase steeply for all galaxies. Quenching timescales for centrals and satellites decrease with stellar mass in this regime to τ Q 2 Gyr. In anticipation of new intermediate redshift observational galaxy surveys, we analyse the passive and star-forming fractions of galaxies across redshift, and find that the τ Q peak at intermediate stellar masses is responsible for a peak (inflection point) in the fraction of green valley central (satellite) galaxies at z ≈ 0.5 − 0.7.

We use a sample of z = 0 galaxies visually classified as slow rotators (SRs) in the eagle hydrodynamical simulations to explore the effect of galaxy mergers on their formation, characterise their intrinsic galaxy properties, and study the connection between quenching and kinematic transformation. SRs that have had major or minor mergers (mass ratios ≥0.3 and 0.1 − 0.3, respectively) tend to have a higher triaxiality parameter and ex-situ stellar fractions than those that had exclusively very minor mergers or formed in the absence of mergers (“no-merger” SRs). No-merger SRs are more compact, have lower black hole-to-stellar mass ratios and quenched later than other SRs, leaving imprints on their z = 0 chemical composition. For the vast majority of SRs we find that quenching, driven by active galactic nuclei feedback, precedes kinematic transformation, except for satellite SRs, in which these processes happen in tandem. However, in ≈50 per cent of these satellites, satellite-satellite mergers are responsible for their SR fate, while environment (i.e. tidal field and interactions with the central) can account for the transformation in the rest. By splitting SRs into kinematic sub-classes, we find that flat SRs prefer major mergers; round SRs prefer minor or very minor mergers; prolate SRs prefer gas-poor mergers. Flat and prolate SRs are more common among satellites hosted by massive haloes ($&gt;10^{13.6}\, \rm M_{\odot }$) and centrals of high masses ($M_{\star } &gt; 10^{10.5}\, \rm M_{\odot }$). Although eagle galaxies display kinematic properties that broadly agree with observations, there are areas of disagreement, such as inverted stellar age and velocity dispersion profiles. We discuss these and how upcoming simulations can solve them.