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arXiv · 1710.08422

On the nature and physical conditions of the luminous Lya emitter CR7 and its rest-frame UV components

David Sobral·Jorryt Matthee·Gabriel Brammer·Andrea Ferrara·Lara Alegre·Huub Rottgering·Daniel Schaerer·Bahram Mobasher·Behnam Darvish
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Abstract

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$α$ emitter at z=6.6, CR7. Our re-reduced, flux calibrated X-SHOOTER spectra of CR7 reveal a HeII emission line in observations obtained along the major axis of Lyman-alpha (Lya) emission with the best seeing conditions. HeII is spatially offset by +0.8'' from the peak of Lya 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 $β=-2.5^{+0.6}_{-0.7}$ 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 (~2.2$σ$) 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 <2x10$^{-17}$ erg s$^{-1}$ cm$^{-2}$ (3 $σ$). 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 ~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.

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David Sobral, Jorryt Matthee, Gabriel Brammer, Andrea Ferrara, Lara Alegre, Huub Rottgering, Daniel Schaerer, Bahram Mobasher, Behnam Darvish. 2018-10-10. On the nature and physical conditions of the luminous Lya emitter CR7 and its rest-frame UV components. https://doi.org/10.1093/mnras%2Fsty2779

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