We present new HST /WFC3 observations and re-analyse VLT data to unveil the continuum , variability and rest-frame UV lines of the multiple UV clumps of the most luminous Ly \alpha emitter at z = 6.6 , CR7 .
Our re-reduced , flux calibrated X-SHOOTER spectra of CR7 reveal a He ii emission line in observations obtained along the major axis of Ly \alpha emission with the best seeing conditions .
He ii is spatially offset by \approx + 0.8 ^ { \prime \prime } from the peak of Ly \alpha emission , and it is found towards clump B .
Our WFC3 grism spectra detects the UV continuum of CR7 ’ s clump A , yielding a power law with \beta = -2.5 ^ { +0.6 } _ { -0.7 } and M _ { UV } = -21.87 ^ { +0.25 } _ { -0.20 } .
No significant variability is found for any of the UV clumps on their own , but there is tentative ( \approx 2.2 \sigma ) brightening of CR7 in F110W as a whole from 2012 to 2017 . HST grism data fail to robustly detect rest-frame UV lines in any of the clumps , implying fluxes ~ { } \lower 2.15 pt \hbox { $ \buildrel < \over { \sim } $ } ~ { } 2 \times 10 ^ { -17 } erg s ^ { -1 } cm ^ { -2 } ( 3 \sigma ) .
We perform cloudy modelling to constrain the metallicity and the ionising nature of CR7 .
CR7 seems to be actively forming stars without any clear AGN activity in clump A , consistent with a metallicity of \sim 0.05 - 0.2 Z _ { \odot } .
Component C or an inter-clump component between B and C may host a high ionisation source .
Our results highlight the need for spatially resolved information to study the formation and assembly of early galaxies .