Abstract

The deflection angles of lensed sources increase with their distance behind a given lens. We utilize this geometric effect to corroborate the z(phot) similar or equal to 9.8 photometric redshift estimate of a faint near-IR dropout, triply imaged by the massive galaxy cluster A2744 in deep Hubble Frontier Fields images. The multiple images of this source follow the same symmetry as other nearby sets of multiple images that bracket the critical curves and have well-defined redshifts (up to z(spec) similar or equal to 3.6), but with larger deflection angles, indicating that this source must lie at a higher redshift. Similarly, our different parametric and non-parametric lens models all require this object be at z greater than or similar to 4, with at least 95% confidence, thoroughly excluding the possibility of lower-redshift interlopers. To study the properties of this source, we correct the two brighter images for their magnifications, leading to a star formation rate of similar to 0.3M(circle dot) yr(-1), a stellar mass of similar to 4 x 10(7) M-circle dot, and an age of less than or similar to 220 Myr (95% confidence). The intrinsic apparent magnitude is 29.9 AB (F160W), and the rest-frame UV (similar to 1500 angstrom) absolute magnitude is M-UV,M-AB = -17.6. This corresponds to similar to 0.1L(z=8)(*) (similar to 0.2 L-z=10(*), adopting dM(*)/dz similar to 0.45), making this candidate one of the least luminous galaxies discovered at z similar to 10.