paper

Geometric Corroboration of the Earliest Lensed Galaxy at z~10.8 from Robust Free-Form Modelling

arXiv:1608.06942 · doi:10.3847/1538-4357/835/1/44

Abstract

A multiply-lensed galaxy, MACS0647-JD, with a probable photometric redshift of is claimed to constitute one of the very earliest known galaxies, formed well before reionization was completed. However, spectral evidence that MACS0647-JD lies at high redshift has proven infeasible and so here we seek an independent lensing based "geometric redshift" derived from the angles between the three lensed images of MACS0647-JD, using our free-form mass model (WSLAP+) for the lensing cluster MACSJ0647.7+7015 (at ). Our lens model uses the 9 sets of multiple images, including those of MACS0647-JD, identified by the CLASH survey towards this cluster. We convincingly exclude the low redshift regime of , for which convoluted critical curves are generated by our method, as the solution bends to accommodate the wide angles of MACS0647-JD for this low redshift. Instead, a best fit to all sets of lensed galaxy positions and redshifts provides a geometric redshift of for MACS0647-JD, strongly supporting the higher photometric redshift solution. Importantly, we find a tight linear relation between the relative brightnesses of all 9 sets of multiply lensed images and their relative magnifications as predicted by our model. This agreement provides a benchmark for the quality of the lens model, and establishes the robustness of our free-form lensing method for measuring model-independent geometric source distances and for deriving objective central cluster mass distributions. After correcting for its magnification the luminosity of MACS0647-JD remains relatively high at , which is within a factor of a few in flux of some surprisingly luminous -- candidates discovered recently in Hubble black field surveys.

23 pages, 22 figures. Accepted by ApJ on 22nd Nov 2016. arXiv admin note: text overlap with arXiv:1406.2702

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