Galaxy And Mass Assembly (GAMA): Timescales for galaxies crossing the
  green valley
  We explore the constraints that can be placed on the evolutionary timescales
for typical low redshift galaxies evolving from the blue cloud through the
green valley and onto the red sequence. We utilise galaxies from the GAMA
survey with 0.1 < z < 0.2 and classify them according to the intrinsic (u-r?)
colours of their stellar populations, as determined by fits to their
multi-wavelength spectral energy distributions. Using these fits to also
determine stellar population ages and star formation timescales, we argue that
our results are consistent with a green valley population dominated by galaxies
that are simply decreasing their star formation (running out of gas) over a
timescale of 2-4 Gyr which are seen at a specific epoch in their evolution
(approximately 1.6 e-folding times after their peak in star formation). If
their fitted star formation histories are extrapolated forwards, the green
galaxies will further redden over time, until they attain the colours of a
passive population. In this picture, no specific quenching event which cuts-off
their star formation is required, though it remains possible that the decline
in star formation in green galaxies may be expedited by internal or external
forces. However, there is no evidence that green galaxies have recently changed
their star formation timescales relative to their previous longer term star
formation histories.
