  The physical and chemical properties of the circumgalactic medium (CGM) at
$z\gtrsim6$ have been studied successfully through the absorption in the
spectra of background Quasi-Stellar Objects (QSOs). One of the most crucial
questions is to investigate the nature and location of the source galaxies that
give rise to these early metal absorbers. Theoretical models suggest that
momentum-driven outflows from typical star-forming galaxies can eject metals
into the CGM and the intergalactic medium (IGM) at z=5-6. Deep, dedicated
surveys have searched for Ly$\alpha$ emission associated with strong CIV
absorbers at $z\approx 6$, but only a few Ly$\alpha$ emitter candidates have
been detected. Interpreting these detections is moreover ambiguous because
Ly$\alpha$ is a resonant line, raising the need for complementary techniques
for detecting absorbers' host galaxies. Here, using Atacama Large Millimeter
Array (ALMA), we report a [C II] 158$\mu$m emitter associated with a strong
low-ionization absorber, OI, at $z=5.978$. The projected impact parameter
between OI and [C II] emitter is 20.0 kpc. The measured [C II] luminosity is
$7.0\times 10^7$ solar luminosities. Further analysis indicates that strong OI
absorbers may reside in the circumgalactic medium of massive halos one to two
orders of magnitude more massive than expected values.
