Satellite content and quenching of star formation in galaxy groups at
  z~1.8
  We study the properties of satellites in the environment of massive
star-forming galaxies at z~1.8 in the COSMOS field, using a sample of 215
galaxies on the main sequence of star formation with an average mass of 10^11
Msun. At z>1.5, these galaxies typically trace halos of mass >10^13 Msun. We
use optical-near-infrared photometry to estimate stellar masses and star
formation rates (SFR) of centrals and satellites down to ~6*10^9 Msun. We stack
data around 215 central galaxies to statistically detect their satellite halos,
finding an average of ~3 galaxies in excess of the background density. We fit
the radial profiles of satellites with simple beta-models, and compare their
integrated properties to model predictions. We find that the total stellar mass
of satellites amounts to 68% of the central galaxy, while SED modeling and
far-infrared photometry consistently show their total SFR to be 25-35% of the
central's rate. We also see significant variation in the specific SFR of
satellites within the halo with, in particular, a sharp decrease at <100 kpc.
After considering different potential explanations, we conclude that this is
likely an environmental signature of the hot inner halo. This effect can be
explained in the first order by a simple free-fall scenario, suggesting that
these low-mass environments can shut down star formation in satellites on
relatively short timescales of ~0.3 Gyr.
