Q1549-C25: A Clean Source of Lyman-Continuum Emission at $z=3.15$

TL;DR

This paper reports the discovery of a rare, clean Lyman-continuum emitting galaxy at z=3.15, providing valuable insights into the escape of ionizing radiation from early galaxies.

Contribution

It presents a detailed analysis of a unique galaxy with confirmed LyC emission, including spectroscopic and imaging data, and estimates its escape fraction of ionizing photons.

Findings

Confirmed LyC emission with no contamination

Estimated escape fraction f_esc(LyC) >= 0.51

Derived galaxy properties: age ~1 Gyr, stellar mass 7.9x10^9 M_sun

Abstract

We present observations of Q1549-C25, an ~L* star-forming galaxy at z=3.15 for which Lyman-continuum (LyC) radiation is significantly detected in deep Keck/LRIS spectroscopy. We find no evidence for contamination from a lower-redshift interloper close to the line of sight in the high signal-to-noise spectrum of Q1549-C25. Furthermore, the morphology of Q1549-C25 in V_606, J_125, and H_160 Hubble Space Telescope (HST) imaging reveals that the object consists of a single, isolated component within 1". In combination, these data indicate Q1549-C25 as a clean spectroscopic detection of LyC radiation, only the second such object discovered to date at z~3. We model the spectral energy distribution (SED) of Q1549-C25, finding evidence for negligible dust extinction, an age (assuming continuous star formation) of ~1 Gyr, and a stellar mass of M_*=7.9x10^9 M_sun. Although it is not possible to derive strong constraints on the absolute escape fraction of LyC emission, f_esc(LyC), from a single object, we use simulations of intergalactic and circumgalactic absorption to infer f_esc(LyC)>=0.51 at 95% confidence. The combination of deep Keck/LRIS spectroscopy and HST imaging is required to assemble a larger sample of objects like Q1549-C25, and obtain robust constraints on the average f_esc(LyC) at z~3 and beyond.