The unexpectedly large dust and gas content of quiescent galaxies at
  z>1.4
  Early type galaxies (ETG) contain most of the stars present in the local
Universe and, above a stellar mass of ~5e10 Msun, vastly outnumber spiral
galaxies like the Milky Way. These massive spheroidal galaxies have, in the
present day, very little gas or dust, and their stellar populations have been
evolving passively for over 10 billion years. The physical mechanisms that led
to the termination of star formation in these galaxies and depletion of their
interstellar medium remain largely conjectural. In particular, there are
currently no direct measurements of the amount of residual gas that might be
still present in newly quiescent spheroids at high redshift. Here we show that
quiescent ETGs at z~1.8, close to their epoch of quenching, contained 2-3
orders of magnitude more dust at fixed stellar mass than local ETGs. This
implies the presence of substantial amounts of gas (5-10%), which was however
consumed less efficiently than in more active galaxies, probably due to their
spheroidal morphology, and consistently with our simulations. This lower star
formation efficiency, and an extended hot gas halo possibly maintained by
persistent feedback from an active galactic nucleus (AGN), combine to keep ETGs
mostly passive throughout cosmic time.
