Lyman continuum leaking from the compact star-forming dwarf galaxy J0925+1403

TL;DR

This study identifies a nearby low-mass star-forming galaxy, J0925+1403, that leaks ionising radiation with an escape fraction of about 8%, providing insights into sources responsible for cosmic reionisation.

Contribution

It presents the first direct detection of significant ionising radiation escape from a low-redshift galaxy, serving as a local proxy for early universe reionisation sources.

Findings

J0925+1403 has an escape fraction of ~8%.

The galaxy's ionising photons can reionise a mass 40 times its stellar mass.

This is one of the few low-redshift galaxies with detected ionising radiation escape.

Abstract

One of the key questions in observational cosmology is the identification of the sources responsible for ionisation of the Universe after the cosmic Dark Ages, when the baryonic matter was neutral. The currently identified distant galaxies are insufficient to fully reionise the Universe by redshift z~6, but low-mass star-forming galaxies are thought to be responsible for the bulk of the ionising radiation. Since direct observations at high redshift are difficult for a variety of reasons, one solution is to identify local proxies of this galaxy population. However, starburst galaxies at low redshifts are generally opaque to their ionising radiation. This radiation with small escape fractions of 1-3% is directly detected only in three low-redshift galaxies. Here we present far-ultraviolet observations of a nearby low-mass star-forming galaxy, J0925+1403, selected for its compactness and high excitation. The galaxy is leaking ionising radiation, with an escape fraction of ~8%. The total number of photons emitted during the starburst phase is sufficient to ionize intergalactic medium material, which is about 40 times more massive than the stellar mass of the galaxy.