Abstract
We report new deep ALMA observations aimed at investigating the CII158um
line and continuum emission in three spectroscopically confirmed Lyman Break
Galaxies at 6.8<z<7.1, i.e. well within the re-ionization epoch. With Star
Formation Rates of SFR ~ 10 Msun/yr these systems are more representative of
the high-z galaxy population than the extreme ones targeted in the past by
millimeter observations. At the location of the optical emission, tracing both
the Lyalpha line and the far-UV continuum, no CII emission is detected.
However, for the galaxy with the deepest observation we detect CII emission
at redshift z=7.107, fully consistent with the Lyalpha redshift, but spatially
offset by 0.7" (4 kpc) from the optical emission. These results support
expectations from recent models that molecular clouds in the central parts of
primordial galaxies are rapidly disrupted by stellar feedback. As a result,
CII emission mostly arises from more external accreting/satellite clumps of
neutral gas. Thermal far-infrared continuum is not detected in any of the three
galaxies. However, the upper limits on the infrared-to-UV emission ratio do not
exceed those derived in metal- and dust-poor galaxies.
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