The anatomy of an extreme starburst within 1.3Gyr of the Big Bang
  revealed by ALMA
  We present further analysis of the [CII] 158$\mu$m fine structure line and
thermal dust continuum emission from the archetype extreme starburst/AGN group
of galaxies in the early Universe, BRI 1202-0725 at $z=4.7$, using the Atacama
Large Millimeter Array. The group is long noted for having a closely separated
(26kpc in projection) FIR-hyperluminous quasar host galaxy and an optically
obscured submm galaxy (SMG). A short ALMA test observation reveals a rich
laboratory for the study of the myriad processes involved in clustered massive
galaxy formation in the early Universe. Strong [CII] emission from the SMG and
the quasar have been reported earlier by Wagg et al. (2012) based on these
observations. In this letter, we examine in more detail the imaging results
from the ALMA observations, including velocity channel images,
position-velocity plots, and line moment images. We present detections of [CII]
emission from two Ly$\alpha$-selected galaxies in the group, demonstrating the
relative ease with which ALMA can detect the [CII] emission from lower star
formation rate galaxies at high redshift. Imaging of the [CII] emission shows a
clear velocity gradient across the SMG, possibly indicating rotation or a more
complex dynamical system on a scale $\sim 10$kpc. There is evidence in the
quasar spectrum and images for a possible outflow toward the southwest, as well
as more extended emission (a 'bridge'), between the quasar and the SMG,
although the latter could simply be emission from Ly$\alpha$-1 blending with
that of the quasar at the limited spatial resolution of the current
observations. These results provide an unprecedented view of a major merger of
gas rich galaxies driving extreme starbursts and AGN accretion during the
formation of massive galaxies and supermassive black holes within 1.3 Gyr of
the Big Bang.
