ALMA Imaging of Gas and Dust in a Galaxy Protocluster at Redshift 5.3:
  [CII] Emission in "Typical" Galaxies and Dusty Starbursts ~1 Billion Years
  after the Big Bang
  We report interferometric imaging of [CII] and OH emission toward the center
of the galaxy protocluster associated with the z=5.3 submillimeter galaxy (SMG)
AzTEC-3, using the Atacama Large (sub)Millimeter Array (ALMA). We detect strong
[CII], OH, and rest-frame 157.7 um continuum emission toward the SMG. The [CII]
emission is distributed over a scale of 3.9 kpc, implying a dynamical mass of
9.7 x 10^10 Msun, and a star formation rate (SFR) surface density of Sigma_SFR
= 530 Msun/yr/kpc2. This suggests that AzTEC-3 forms stars at Sigma_SFR
approaching the Eddington limit for radiation pressure supported disks. We find
that the OH emission is slightly blueshifted relative to the [CII] line, which
may indicate a molecular outflow associated with the peak phase of the
starburst. We also detect and dynamically resolve [CII] emission over a scale
of 7.5 kpc toward a triplet of Lyman-break galaxies with moderate UV-based SFRs
in the protocluster at ~95kpc projected distance from the SMG. These galaxies
are not detected in the continuum, suggesting far-infrared SFRs of <18-54
Msun/yr, consistent with a UV-based estimate of 22 Msun/yr. The spectral energy
distribution of these galaxies is inconsistent with nearby spiral and starburst
galaxies, but resembles those of dwarf galaxies. This is consistent with
expectations for young starbursts without significant older stellar
populations. This suggests that these galaxies are significantly
metal-enriched, but not heavily dust-obscured, "normal" star-forming galaxies
at z>5, showing that ALMA can detect the interstellar medium in "typical"
galaxies in the very early universe.
