Resolving Clumpy versus Extended Lyα in Strongly Lensed, High-redshift Lyα Emitters

Abstract

We present six strongly gravitationally lensed Ly α emitters (LAEs) at z ∼ 4–5 with Hubble Space Telescope (HST) narrowband imaging isolating Ly α . Through complex radiative transfer Ly α encodes information about the spatial distribution and kinematics of the neutral hydrogen upon which it scatters. We investigate the galaxy properties and Ly α morphologies of our sample. Many previous studies of high-redshift LAEs have been limited in Ly α spatial resolution. In this work we take advantage of high-resolution Ly α imaging boosted by lensing magnification, allowing us to probe subgalactic scales that are otherwise inaccessible at these redshifts. We use broadband imaging from HST (rest-frame UV) and Spitzer (rest-frame optical) in spectral energy distribution fitting, providing estimates of the stellar masses (∼10 8 –10 9 M ⊙ ), stellar population ages ( t 50 < 40 Myr), and amounts of dust ( A V ∼ 0.1–0.6, statistically consistent with zero). We employ nonparametric star formation histories to probe the young stellar populations which create the Ly α . We also examine the offsets between the Ly α and stellar continuum, finding small upper limits of offsets (<0.″1) consistent with studies of low-redshift LAEs, indicating our galaxies are not interacting or merging. Finally, we find a bimodality in our sample’s Ly α morphologies: clumpy and extended. We find a suggestive trend: our LAEs with clumpy Ly α are generally younger than the LAEs with extended Ly α , suggesting a possible correlation with age.