Efficient satellite quenching at z~1 from the GEEC2 spectroscopic survey
  of galaxy groups
  We present deep GMOS-S spectroscopy for 11 galaxy groups at 0.8<z<1.0, for
galaxies with r_{AB}<24.75. Our sample is highly complete (>66%) for eight of
the eleven groups. Using an optical-NIR colour-colour diagram, the galaxies in
the sample were separated with a dust insensitive method into three categories:
passive (red), star-forming (blue), and intermediate (green). The strongest
environmental dependence is observed in the fraction of passive galaxies, which
make up only ~20 per cent of the field in the mass range
10^{10.3}<M_{star}/M_\odot<10^{11.0} but are the dominant component of groups.
If we assume that the properties of the field are similar to those of the
`pre-accreted' population, the environment quenching efficiency (\epsilon_\rho)
is defined as the fraction of field galaxies required to be quenched in order
to match the observed red fraction inside groups. The efficiency obtained is
~0.4, similar to its value in intermediate-density environments locally. While
green (intermediate) galaxies represent ~20 per cent of the star-forming
population in both the group and field, at all stellar masses, the average sSFR
of the group population is lower by a factor of ~3. The green population does
not show strong H-delta absorption that is characteristic of starburst
galaxies. Finally, the high fraction of passive galaxies in groups, when
combined with satellite accretion models, require that most accreted galaxies
have been affected by their environment. Thus, any delay between accretion and
the onset of truncation of star formation (\tau) must be <2 Gyr, shorter than
the 3-7 Gyr required to fit data at z=0. The relatively small fraction of
intermediate galaxies requires that the actual quenching process occurs
quickly, with an exponential decay timescale of \tau_q<1 Gyr.
