The physical origin of low escape fractions of ionizing radiation derived from Lyman-break galaxies ( LBGs ) at z \sim 3 – 4 is not well understood .
We perform idealised disc galaxy simulations to understand how galactic properties such as metallicity and gas mass affect the escape of Lyman Continuum ( LyC ) photons using radiation-hydrodynamic simulations with strong stellar feedback .
We find that the luminosity-weighted escape fraction from a metal-poor ( Z = 0.002 ) galaxy embedded in a halo of mass M _ { h } \simeq 10 ^ { 11 } M _ { \odot } is \left < \mbox { $f _ { esc } ^ { 3 D } $ } \right > \simeq 7 \% .
Roughly half of the LyC photons are absorbed within scales of 100 pc , and the other half is absorbed in the ISM ( \la 2 { kpc } ) .
When the metallicity of the gas is increased to Z = 0.02 , the escape fraction is significantly reduced to \left < \mbox { $f _ { esc } ^ { 3 D } $ } \right > \simeq 1 \% because young stars are enshrouded by their birth clouds for a longer time .
In contrast , increasing the gas mass by a factor of 5 leads to \left < \mbox { $f _ { esc } ^ { 3 D } $ } \right > \simeq 4 \% because LyC photons are only moderately absorbed by the thicker disc .
Our experiments suggest that high metallicity is likely more responsible for the low escape fractions observed in LBGs , supporting the scenario in which the escape fraction is decreasing with increasing halo mass .
Finally , negligible correlation is observed between the escape fraction and surface density of star formation or galactic outflow rates .