The role of stochastic and smooth processes in regulating galaxy
  quenching
  Galaxies can be classified as passive ellipticals or star-forming discs.
Ellipticals dominate at the high end of the mass range, and therefore there
must be a mechanism responsible for the quenching of star-forming galaxies.
This could either be due to the secular processes linked to the mass and star
formation of galaxies or to external processes linked to the surrounding
environment. In this paper, we analytically model the processes that govern
galaxy evolution and quantify their contribution. We have specifically studied
the effects of mass quenching, gas stripping, and mergers on galaxy quenching.
To achieve this, we first assumed a set of differential equations that describe
the processes that shape galaxy evolution. We then modelled the parameters of
these equations by maximising likelihood. These equations describe the
evolution of galaxies individually, but the parameters of the equations are
constrained by matching the extrapolated intermediate-redshift galaxies with
the low-redshift galaxy population. In this study, we modelled the processes
that change star formation and stellar mass in massive galaxies from the GAMA
survey between z~0.4 and the present. We identified and quantified the
contributions from mass quenching, gas stripping, and mergers to galaxy
quenching. The quenching timescale is on average 1.2 Gyr and a closer look
reveals support for the slow-then-rapid quenching scenario. The major merging
rate of galaxies is about once per 10~Gyr, while the rate of ram pressure
stripping is significantly higher. In galaxies with decreasing star formation,
we show that star formation is lost to fast quenching mechanisms such as ram
pressure stripping and is countered by mergers, at a rate of about 41%
Gyr$^{-1}$ and to mass quenching 49% Gyr$^{-1}$. (abridged)
