James Webb Space Telescope Feed Post

The nature of an ultra-faint galaxy in the cosmic Dark Ages seen with JWST

A false-colour NIRCam image of the Abell 2744 cluster. Critical curves of formally infinite magnification from two lensing models ([5] and an update to [3], discussed in the Methods section) are plotted as blue and cyan curves ([5] in blue and the [3] update in cyan). The A, B and C multiple images of the z = 9.79 galaxy are highlighted by red circles. The inset plots represent zoom-ins on each of the triply-imaged components, with the brightest component (JD1) highlighted by the 0.''2 × 1.''2 NIRSpec slit (constructed using three MSA shutters) used for prism spectroscopy in our DDT programme. Critical lines for a source at z ~ 10 , the redshift indicated by the lens model, the photometry and the spectroscopy, are in excellent mutual agreement – highlighting the robustness of the lens model – and fall between the two images consistent with their similar brightness. To show the power of lensing to constrain the redshift of the source, we also show, as an orange line, the critical line for a source at z = 2.245. If JD1 were at this lower redshift, the image positions and fluxes would be inconsistent with the measurements. Here B=F115W+F150W, G=F200W+F277W, R=F356W+F444W