Detecting galaxies when their star-formation is being quenched is crucial to understand the mechanisms driving their evolution .
We identify for the first time a sample of quenching galaxies selected just after the interruption of their star formation by exploiting the [ \ion Oiii ] \lambda 5007 /H \alpha ratio and searching for galaxies with undetected [ \ion OIII ] .
Using a sample of \sim 174000 star-forming galaxies extracted from the SDSS-DR8 at 0.04 ~ { } \leq~ { } \text { z } ~ { } < ~ { } 0.21 , we identify the \sim 300 quenching galaxy best candidates with low [ \ion Oiii ] /H \alpha , out of \sim 26 ~ { } 000 galaxies without [ \ion Oiii ] emission .
They have masses between 10 ^ { 9.7 } and 10 ^ { 10.8 } M { { } _ { \odot } } , consistently with the corresponding growth of the quiescent population at these redshifts .
Their main properties ( i.e .
star-formation rate , colours and metallicities ) are comparable to those of the star-forming population , coherently with the hypothesis of recent quenching , but preferably reside in higher-density environments.Most candidates have morphologies similar to star-forming galaxies , suggesting that no morphological transformation has occurred yet .
From a survival analysis we find a low fraction of candidates ( \sim 0.58 % of the star-forming population ) , leading to a short quenching timescale of t _ { Q } \sim 50 Myr and an e -folding time for the quenching history of \tau _ { Q } \sim 90 Myr , and their upper limits of t _ { Q } < 0.76 Gyr and \tau _ { Q } < 1.5 Gyr , assuming as quenching galaxies 50 % of objects without [ \ion Oiii ] ( \sim 7.5 \% ) .Our results are compatible with a ’ rapid ’ quenching scenario of satellites galaxies due to the final phase of strangulation or ram-pressure stripping .
This approach represents a robust alternative to methods used so far to select quenched galaxies ( e.g .
colours , specific star-formation rate , or post-starburst spectra ) .