GEOMETRIC CORROBORATION of the EARLIEST LENSED GALAXY at z ≃ 10.8 from ROBUST FREE-FORM MODELLING

Brian M.Y. Chan, Tom Broadhurst, Jeremy Lim, Jose M. Diego, Adi Zitrin, Dan Coe, Holland C. Ford

Research output: Contribution to journalReview articlepeer-review

12 Scopus citations

Abstract

A multiply lensed galaxy, MACS0647-JD, with a probable photometric redshift of z ≃ 10.7+0.6 -0.4 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 MUV = -19.4, which is within a factor of a few in flux of some surprisingly luminous z ≃10-11 candidates discovered recently in Hubble blank field surveys.

Original languageEnglish
Article number44
JournalAstrophysical Journal
Volume835
Issue number1
DOIs
StatePublished - 20 Jan 2017
Externally publishedYes

Keywords

  • dark matter
  • galaxies: high-redshift
  • gravitational lensing: strong

ASJC Scopus subject areas

  • Astronomy and Astrophysics
  • Space and Planetary Science

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