Galaxy Formation Through Filamentary Accretion at z=6.1
  We present ALMA observations of the dust continuum and [C II] 158um line
emission from the z=6.0695 Lyman Break Galaxy WMH5. These observations at 0.3"
spatial resolution show a compact (~3kpc) main galaxy in dust and [C II]
emission, with a 'tail' of emission extending to the east by about 5kpc (in
projection). The [C II] tail is comprised predominantly of two distinct
sub-components in velocity, separated from the core by ~100 and 250km/s, with
narrow intrinsic widths of about 80km/s, which we call 'sub-galaxies'. The
sub-galaxies themselves are extended east-west by about 3kpc in individual
channel images. The [C II] tail joins smoothly into the main galaxy velocity
field. The [C II] line to continuum ratios are comparable for the main and
sub-galaxy positions, within a factor 2. In addition, these ratios are
comparable to z~5.5 LBGs. We conjecture that the WMH5 system represents the
early formation of a galaxy through the accretion of smaller satellite
galaxies, embedded in a smoother gas distribution, along a possibly filamentary
structure. The results are consistent with current cosmological simulations of
early galaxy formation, and support the idea of very early enrichment with dust
and heavy elements of the accreting material.
