Evolution of the Gas Mass Fraction of Progenitors to Today's Massive
  Galaxies: ALMA Observations in the CANDELS GOODS-S Field
  We present an ALMA survey of dust continuum emission in a sample of 70
galaxies in the redshift range z=2-5 selected from the CANDELS GOODS-S field.
Multi-Epoch Abundance Matching (MEAM) is used to define potential progenitors
of a z = 0 galaxy of stellar mass 1.5 10^11 M_sun. Gas masses are derived from
the 850um luminosity. Ancillary data from the CANDELS GOODS-S survey are used
to derive the gas mass fractions. The results at z<=3 are mostly in accord with
expectations: The detection rates are 75% for the z=2 redshift bin, 50% for the
z=3 bin and 0% for z>=4. The average gas mass fraction for the detected z=2
galaxies is f_gas = 0.55+/-0.12 and f_gas = 0.62+/-0.15 for the z=3 sample.
This agrees with expectations for galaxies on the star-forming main sequence,
and shows that gas fractions have decreased at a roughly constant rate from z=3
to z=0. Stacked images of the galaxies not detected with ALMA give upper limits
to f_gas of <0.08 and <0.15, for the z=2 and z=3 redshift bins. None of our
galaxies in the z=4 and z=5 sample are detected and the upper limit from
stacked images, corrected for low metallicity, is f_gas<0.66. We do not think
that lower gas-phase metallicities can entirely explain the lower dust
luminosities. We briefly consider the possibility of accretion of very
low-metallicity gas to explain the absence of detectable dust emission in our
galaxies at z>4.
