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

Kavli Affiliate: Robert Simcoe

| First 5 Authors: T. Emil Rivera-Thorsen, Håkon Dahle, Max Gronke, Matthew Bayliss, Jane Rigby

| Summary:

We present rest-frame ultraviolet and optical spectroscopy of the brightest
lensed galaxy yet discovered, at redshift z = 2.4. This source reveals a
characteristic, triple-peaked Lyman {alpha} profile which has been predicted
by 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 {alpha}
photons; but 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 apart from 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.

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