Escaping ionizing photons from massive spiral galaxies at $z\sim 1$

TL;DR

This study reports the first detection of Lyman continuum photons from massive spiral galaxies at z~1, suggesting galaxy orientation influences LyC escape, with implications for understanding ionizing photon leakage in disk galaxies.

Contribution

It provides the first evidence linking galaxy orientation to LyC detectability in high-redshift spiral galaxies, highlighting geometric and feedback effects on photon escape.

Findings

Detection of LyC photons from three massive spiral galaxies at z~1.

Face-on orientation may increase LyC detection likelihood.

Galaxy feedback and geometry influence ionizing photon escape.

Abstract

We report the detection of Lyman continuum (LyC) photons from three massive ($\text{M}_{*}>10^{10}\:\text{M}_{\odot}$) spiral galaxies at a redshift of nearly 1 in the AstroSat UV Deep Field South. Notably, all three systems are viewed at low inclination (i.e., nearly face-on), prompting an investigation into the role of galaxy orientation in the detectability of LyC emission from disk systems. Two of the three galaxies, however, host active galactic nuclei (AGNs), adding complexity to the interpretation of the LyC signal. We present a detailed analysis of the likely star-forming case, and report tentative evidence that a face-on viewing angle may enhance the likelihood of LyC detection in disk galaxies. This represents the first detection of LyC emission from well-characterized spiral galaxies at high redshift, offering a new window into LyC escape mechanisms in such systems. Our findings highlight the need to consider geometric factors and anisotropic escape pathways facilitated by feedback processes alongside more traditional density-bounded scenarios that imply isotropic escape.