Abstract
Abstract We report the detection of Lyman continuum (LyC) emission from the galaxy, CDFS-6664, at z = 3.797 in a sample of Lyman break galaxies with detected [O iii] emission lines. The LyC emission is detected with a significance ∼5σ in the F336W band of the Hubble Deep UV Legacy Survey, corresponding to the 650–770 Å rest frame. The light centroid of the LyC emission is offset from the galaxy center by about 0.″2 (1.4 pkpc). The Hubble deep images at longer wavelengths show that the emission is unlikely provided by low-redshift interlopers. The photometric and spectroscopic data show that the possible contribution of an active galactic nucleus is quite low. Fitting the spectral energy distribution of this source to stellar population synthesis models, we find that the galaxy is young (∼50 Myr) and actively forming stars with a rate of 52.1 ± 4.9 M ⊙ yr−1. The significant star formation and the spatially offset LyC emission support a scenario where the ionizing photons escape from the low-density cavities in the ISM excavated by massive young stars. From the nebular model, we estimate the escape fraction of LyC photons to be 38% ± 7% and the corresponding intergalactic medium (IGM) transmission to be 60%, which deviates more than 3σ from the average transmission. The unusually high IGM transmission of LyC photons in CDFS-6664 may be related to a foreground type-2 quasar, CDF-202, at z = 3.7, with a projected separation of 1.′2 only. The quasar may have photoevaporated optically thick absorbers and enhance the transmission on the sightline of CDFS-6664.
Highlights
During the epoch of reionization, the neutral and opaque intergalactic medium (IGM) transforms to ionized and transparent
We report the detection of Lyman Continuum (LyC) emission from the galaxy, CDFS-6664, at z = 3.797 in a sample of Lyman break galaxies with detected [OIII] emission lines
We summarize the following aspects suggesting that the source is more likely to be a stellar origin: First, CDFS-6664 is in the sample of the AMAZE project (Maiolino et al 2008; Troncoso et al 2014), in which Lyman break galaxy (LBG) that host AGNs are discarded based on the UV/optical spectra, X-ray data or the MIPS 24μm fluxes
Summary
During the epoch of reionization, the neutral and opaque intergalactic medium (IGM) transforms to ionized and transparent. In addition to the rest-frame UV data, we use the 3D-HST images from F435W to F160W (Grogin et al 2011; Koekemoer et al 2011; Skelton et al 2014) to analyze the escape fraction of the LyC photons. CDFS-6664 is coincidentally located in a gap region where the total exposure time is only
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