Molecular gas on large circumgalactic scales at z=3.47
  We report ALMA observations of the most massive (star forming) galaxy in the
redshift range 3<z<4 within the whole GOODS-S field. We detect a large
elongated structure of molecular gas around the massive primeval galaxy, traced
by the CO(4-3) emission, and extended over 40 kpc. We infer a mass of the large
gaseous structure of Mgas~2-6x10^11 Msun. About 60% of this mass is not
directly associated with either the central galaxy or its two lower mass
satellites. The CO extended structure is also detected in continuum thermal
emission. The kinematics of the molecular gas shows the presence of different
components, which cannot be ascribed to simple rotation. Furthermore, on even
larger scales, we detect nine additional CO systems within a radius of 250 kpc
from the massive galaxy and mostly distributed in the same direction as the CO
elongated structure found in the central 40 kpc. The stacked images of these CO
systems show detections in the thermal continuum and in the X-rays, suggesting
that these systems are forming stars at a rate of 30-120 Msun/yr. We suggest
that the extended gas structure, combined with its kinematic properties, and
the gas rich star forming systems detected on larger scales, are tracing the
inner and densest regions of large scale accreting streams, feeding the central
massive galaxy. These results corroborate models of galaxy formation, in which
accreting streams are clumpy and undergo some star formation (hence enriching
the streams with metals) even before accreting onto the central galaxy.
