ALMA reveals metals yet no dust within multiple components in CR7
  We present spectroscopic follow-up observations of CR7 with ALMA, targeted at
constraining the infrared (IR) continuum and [CII]$_{158 \mu \rm m}$
line-emission at high spatial resolution matched to the HST/WFC3 imaging. CR7
is a luminous Ly$\alpha$ emitting galaxy at $z=6.6$ that consists of three
separated UV-continuum components. Our observations reveal several
well-separated components of [CII] emission. The two most luminous components
in [CII] coincide with the brightest UV components (A and B), blue-shifted by
$\approx 150$ km s$^{-1}$ with respect to the peak of Ly$\alpha$ emission.
Other [CII] components are observed close to UV clumps B and C and are
blue-shifted by $\approx300$ and $\approx80$ km s$^{-1}$ with respect to the
systemic redshift. We do not detect FIR continuum emission due to dust with a
3$\sigma$ limiting luminosity L$_{\rm IR} (T_d = 35 \rm \, K) <
3.1\times10^{10}$ L$_{\odot}$. This allows us to mitigate uncertainties in the
dust-corrected SFR and derive SFRs for the three UV clumps A, B and C of 28, 5
and 7 M$_{\odot}$ yr$^{-1}$. All clumps have [CII] luminosities consistent
within the scatter observed in the local relation between SFR and L$_{\rm
[CII]}$, implying that strong Ly$\alpha$ emission does not necessarily
anti-correlate with [CII] luminosity. Combining our measurements with the
literature, we show that galaxies with blue UV slopes have weaker [CII]
emission at fixed SFR, potentially due to their lower metallicities and/or
higher photoionisation. Comparison with hydrodynamical simulations suggests
that CR7's clumps have metallicities of $0.1<\rm Z/Z_{\odot}<0.2$. The observed
ISM structure of CR7 indicates that we are likely witnessing the build up of a
central galaxy in the early Universe through complex accretion of satellites.
