Abstract
ABSTRACT We report the detection of Lyα emission at ∼9538 Å in the Keck/DEIMOS and Hubble Space Telescope WFC3 G102 grism data from a triply imaged galaxy at z = 6.846 ± 0.001 behind galaxy cluster MACS J2129.4−0741. Combining the emission line wavelength with broadband photometry, line ratio upper limits, and lens modeling, we rule out the scenario that this emission line is [O ii] at z = 1.57. After accounting for magnification, we calculate the weighted average of the intrinsic Lyα luminosity to be ∼ 1.3 × 10 42 erg s − 1 and Lyα equivalent width to be 74 ± 15 Å. Its intrinsic UV absolute magnitude at 1600 Å is −18.6 ± 0.2 mag and stellar mass ( 1.5 ± 0.3 ) × 10 7 M ⊙ , making it one of the faintest (intrinsic L UV ∼ 0.14 L UV * ) galaxies with Lyα detection at z ∼ 7 to date. Its stellar mass is in the typical range for the galaxies thought to dominate the reionization photon budget at z ≳ 7 ; the inferred Lyα escape fraction is high ( ≳ 10 %), which could be common for sub-L* z ≳ 7 galaxies with Lyα emission. This galaxy offers a glimpse of the galaxy population that is thought to drive reionization, and it shows that gravitational lensing is an important avenue for probing the sub-L* galaxy population.
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