One key problem in astrophysics is understanding how and why galaxies switch off their star formation , building the quiescent population that we observe in the local Universe .
From the GAMA and VIPERS surveys , we use spectroscopic indices to select quiescent and candidate transition galaxies .
We identify potentially rapidly transitioning post-starburst galaxies , and slower transitioning green-valley galaxies .
Over the last 8 Gyrs the quiescent population has grown more slowly in number density at high masses ( \hbox { $ { \mathrm { M } } _ { \ast } $ } > 10 ^ { 11 } \hbox { $ { M _ { { } _ { \odot } } } $ } ) than at intermediate masses ( \hbox { $ { \mathrm { M } } _ { \ast } $ } > 10 ^ { 10.6 } \hbox { $ { M _ { { } _ { \odot } } } $ } ) .
There is evolution in both the post-starburst and green valley stellar mass functions , consistent with higher mass galaxies quenching at earlier cosmic times .
At intermediate masses ( \hbox { $ { \mathrm { M } } _ { \ast } $ } > 10 ^ { 10.6 } \hbox { $ { M _ { { } _ { \odot } } } $ } ) we find a green valley transition time-scale of 2.6 Gyr .
Alternatively , at z \sim 0.7 the entire growth rate could be explained by fast-quenching post-starburst galaxies , with a visibility time-scale of 0.5 Gyr .
At lower redshift , the number density of post-starbursts is so low that an unphysically short visibility window would be required for them to contribute significantly to the quiescent population growth .
The importance of the fast-quenching route may rapidly diminish at z < 1 .
However , at high masses ( \hbox { $ { \mathrm { M } } _ { \ast } $ } > 10 ^ { 11 } \hbox { $ { M _ { { } _ { \odot } } } $ } ) , there is tension between the large number of candidate transition galaxies compared to the slow growth of the quiescent population .
This could be resolved if not all high mass post-starburst and green-valley galaxies are transitioning from star-forming to quiescent , for example if they rejuvenate out of the quiescent population following the accretion of gas and triggering of star formation , or if they fail to completely quench their star formation .