ALMA Reveals Metals yet No Dust within Multiple Components in CR7

Abstract

We present spectroscopic follow-up observations of CR7 with ALMA, targeted at constraining the infrared (IR) continuum and [C ii ] line-emission at high spatial resolution matched to the HST /WFC3 imaging. CR7 is a luminous Ly α emitting galaxy at z  = 6.6 that consists of three separated UV-continuum components. Our observations reveal several well-separated components of [C ii ] emission. The two most luminous components in [C ii ] coincide with the brightest UV components (A and B), blueshifted by km s −1 with respect to the peak of Ly α emission. Other [C ii ] components are observed close to UV clumps B and C and are blueshifted by and ≈80 km s −1 with respect to the systemic redshift. We do not detect FIR continuum emission due to dust with a 3 σ limiting luminosity . 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 yr −1 . All clumps have [C ii ] luminosities consistent within the scatter observed in the local relation between SFR and , implying that strong Ly α emission does not necessarily anti-correlate with [C ii ] luminosity. Combining our measurements with the literature, we show that galaxies with blue UV slopes have weaker [C ii ] emission at fixed SFR, potentially due to their lower metallicities and/or higher photoionization. Comparison with hydrodynamical simulations suggests that CR7's clumps have metallicities of . 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.