Abstract
The escape fraction of Lyman continuum (LyC) photons ($f_esc$) is a key
parameter for determining the sources of cosmic reionization at $z6$. At
these redshifts, owing to the opacity of the intergalactic medium, LyC emission
cannot be measured directly. However LyC leakers during the epoch of
reionization could be identified using indirect indicators, that have been
extensively tested at low and intermediate redshift. These include a high
OIII/OII flux ratio, a high star formation surface density and a compact
size. In this work we present observations of 29 $4.5 z 8$
gravitationally lensed galaxies in the Abell 2744 cluster field. From a
combined analysis of JWST-NIRSpec and NIRCam data we accurately derive their
physical and spectroscopic properties: our galaxies have low masses
$(łog(M_\star)8.5)$, blue UV spectral slopes ($-2.1$), compact
sizes ($r_e 0.3-0.5$ kpc), and high OIII/OII flux ratios. Such
properties are similar to those of low-redshift LyC leakers. Indirectly
inferring the fraction of escaping ionizing photons, we find that more than
80\% of our galaxies have predicted $f_esc$ larger than 0.05, i.e. they would
be considered leakers. The average predicted $f_esc$ of our sample is 0.12,
suggesting that similar galaxies at $z6$ provided a substantial
contribution to cosmic reionization.
Users
Please
log in to take part in the discussion (add own reviews or comments).