CLEAR: Boosted Ly$α$ Transmission of the Intergalactic Medium in UV bright Galaxies

Abstract

Reionization is an inhomogeneous process, thought to begin in small ionized bubbles of the intergalactic medium (IGM) around overdense regions of galaxies. Recent Lyman-alpha (Lyα) studies during the epoch of reionization show growing evidence that ionized bubbles formed earlier around brighter galaxies, suggesting higher IGM transmission of Lyα from these galaxies. We investigate this problem using IR slitless spectroscopy from the Hubble Space Telescope (HST) Wide-Field Camera 3 (WFC3) G102 grism observations of 148 galaxies selected via photometric redshifts at 6.0 < z < 8.2. These galaxies have spectra extracted from the CANDELS Lyα Emission at Reionization (CLEAR) survey. We combine the CLEAR data for 275 galaxies with the Keck/DEIMOS+MOSFIRE dataset from the Texas Spectroscopic Search for Lyα Emission at the End of Reionization Survey. We then constrain the Lyα equivalent-width (EW) distribution at 6.0 < z < 8.2, which is described by an exponential form, dN/dEW ∝ exp(-EW)/W 0 , with the characteristic e-folding scale width (W 0 ). We confirm a significant drop of the Lyα strength (or W 0 ) at z > 6. Furthermore, we compare the redshift evolution of W 0 between galaxies at different UV luminosities. The UV-bright (M UV < −21, or L UV > L * ) galaxies show weaker evolution with a decrease of 0.4 (±0.2) dex in W 0 at z > 6 while UV-faint (M UV > −21, or L UV < L * ) galaxies exhibit a significant drop by a factor of 0.7-0.8 (±0.2) dex in W 0 from z < 6 to z > 6. Our results add to the accumulating evidence that UV-bright galaxies exhibit boosted Lyα transmission in the IGM, suggesting that reionization completes sooner in regions proximate to galaxies of higher UV luminosity.

High Equivalent Width of Hα+[N II] Emission in z~8 Lyman-break Galaxies from IRAC 5.8μm Observations: Evidence for Efficient Lyman-continuum Photon production in the Epoch of Re-ionization

“…Under the assumption that the fraction of escaping LyC photons is approximately similar to that of Lyα emission (e.g., Steidel et al 2018, Izotov et al 2020, the implied f esc ranges between 10% and ≈ 40 − 50% (Figure 5). These estimates are likely upper limits, given the still significant fractions of non-detection particularly for sub-L * galaxies (e.g., Pentericci et al 2014, Jung et al 2021. Thus the preliminary indications from Lyα studies are consistent with the more direct estimates, and reinforce the likely ready availability of adequate reionizing photons from star-forming galaxies for reionization.…”

Scattering of Lyα Photons through the Reionizing Intergalactic Medium: I. Spectral Energy Distribution

“…Indeed, a steep decline in the LAE number density is found above z = 6, contrasting its more gradual evolution at lower redshifts. This decline appears steeper for fainter galaxies (M UV −20) (Malhotra & Rhoads 2004;Ouchi et al 2010;Fontana et al 2010;Stark et al 2011;Pentericci et al 2011;Ono et al 2012;Mallery et al 2012;Curtis-Lake et al 2012;Treu et al 2013;Tilvi et al 2014;Zheng et al 2017;Endsley et al 2021), while the decline appears less dramatic for the brighter ones (Matthee et al 2015;Castellano et al 2018;Jung et al 2019;Harikane et al 2019;Higuchi et al 2019;Jung et al 2020;Tilvi et al 2020;Hu et al 2021;Jung et al 2021), consistent with theoretical expectations for the "inside-out" reionization scenario (e.g., Malhotra & Rhoads 2004;Mason et al 2018;Katz et al 2019;Gronke et al 2021;Park et al 2021;Smith et al 2021a;Qin et al 2021).…”

CLEAR: The Ionization and Chemical-Enrichment Properties of Galaxies at 1.1 < z < 2.3

“…These will be described fully in the forthcoming paper on the data release (Simons et al, in prep. ) and have been discussed in other papers using these data (e.g., Estrada-Carpenter et al 2019, 2020Simons et al 2021;Jung et al 2021;Backhaus et al 2022;Cleri et al 2022;Matharu 2022).…”