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Published January 20, 2017 | Published + Submitted
Journal Article Open

Geometric Corroboration of the Earliest Lensed Galaxy at z ≃ 10.8 from Robust Free-form Modelling

Abstract

A multiply lensed galaxy, MACS0647-JD, with a probable photometric redshift of z ≃ 10.7_(-0.4)^(+0.6) 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 z = 0.591). Our lens model uses the nine sets of multiple images, including those of MACS0647-JD, identified by the CLASH survey toward this cluster. We convincingly exclude the low-redshift regime of z < 3, 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 z≃ 10.8_(-0.4)^(+0.3) for MACS0647-JD, strongly supporting the higher photometric redshift solution. Importantly, we find a tight linear relation between the relative brightnesses of all nine 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 M UV = −19.4, which is within a factor of a few in flux of some surprisingly luminous z sime 10–11 candidates discovered recently in Hubble blank field surveys.

Additional Information

© 2017. The American Astronomical Society. Received 2016 September 15. Accepted 2016 November 16. Published 2017 January 17. The work is based on observations made with the NASA/ESA Hubble Space Telescope and operated by the Association of Universities for Research in Astronomy, Inc. under NASA contract NAS 5-26555. T.J.B. gratefully acknowledges the Visiting Research Professor Scheme at the University of Hong Kong. J.M.D. acknowledges support of the consolider project AYA2015-64508-P (MINECO/FEDER, UE), CAD2010-00064 and AYA2012-39475-C02-01 funded by the Ministerio de Economia y Competitividad, and support from the Department of Physics at The University of Hong Kong for a visit to work on this project. J.L. acknowledges support from the University of Hong Kong via a Seed Funding Program for Basic Research through grant 201411159166 at the start of this project, thus enabling follow-up support from the Research Grants Council of Hong Kong through grant 17319316.

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Published - Chan_2017_ApJ_835_44.pdf

Submitted - 1608.06942v3.pdf

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Created:
August 22, 2023
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October 24, 2023