The Sunburst Arc: Direct Lyman α escape observed in the brightest known lensed galaxy

Abstract

We present rest-frame ultraviolet and optical spectroscopy of the brightest lensed galaxy yet discovered, at redshift z = 2.4. The source reveals a characteristic triple-peaked Lyman α profile that has been predicted in various theoretical works, but to our knowledge has not been unambiguously observed previously. The feature is well fit by a superposition of two components: a double-peak profile emerging from substantial radiative transfer, and a narrow, central component resulting from directly escaping Lyman α photons, but it is poorly fit by either component alone. We demonstrate that the feature is unlikely to contain contamination from nearby sources, and that the central peak is unaffected by radiative transfer effects except for very slight absorption. The feature is detected at signal-to-noise ratios exceeding 80 per pixel at line center, and bears strong resemblance to synthetic profiles predicted by numerical models.

Diverse properties of Ly α emission in low-redshift compact star-forming galaxies with extremely high [O iii]/[O ii] ratios

“…The linear fits to the surface brightness profiles of the outer galaxy parts are shown by solid lines. and two z > 2 LyC leakers (Vanzella et al 2018;Rivera-Thorsen et al 2017). However, at variance with J1032+4919, all other triple-peaked spectra in the literature do not show clear signs of underlying Lyα absorption.…”

HST Imaging of the Ionizing Radiation from a Star-forming Galaxy at z = 3.794

“…The properties of low-ionization interstellar lines vary among the LyC emitters. While the absorption features such as Si IIλ1260, O Iλ1303 and C IIλ1334 are very weak or even absent in Ion2 Vanzella et al 2016) and Ion3 (Vanzella et al 2018), they are clearly observed in the Sunburst (Si IIλ1260, Rivera-Thorsen et al 2017 Shapley et al 2016), and Ion1 (see Figure 2). The scattering of the low-ionization absorption properties among the emitters suggests that the conditions under which ionizing radiation can escape from host galaxies are local, namely LyC photons can escape if there exists low neutral gas covering holes in the surrounding where the ionizing emission arise (the 1D spectrum of a galaxy is basically a luminosity-weighted average).…”

Gravitational lensing reveals ionizing ultraviolet photons escaping from a distant galaxy

“…Because the assumption of the Reddy law with the STARBURST99 models yields an escape fraction as high as 93%, we conclude that the dust attenuation curve for the Sunburst Arc is indeed likely to be well approximated by the Reddy law. (13). Overlaid are theoretical and empirical stellar/AGN separation lines (49,55).…”

“…S1). The Lyman-α profile indicated that it was a prime candidate for strong LyC escape through a narrow channel oriented towards Earth (13). Such a LyC channel should appear as a multiply-imaged, compact source coincident with some of the brightest regions seen in the extended, non-ionizing stellar continuum (19) when observed using telescopes with sufficient resolution and ultraviolet capabilities.…”