The Effect of Galactic Properties on the Escape Fraction

摘要

Understanding the escape fractionfrom early galaxies gives an important constraint on the sources that reionize the universe. Previous studies of f_(esc) have found a wide range of values, varying from less than 0.01 to nearly L Rather than try to find an exact value of f_(esc), we seek to understand how internal properties of the galaxy affect f_(esc). Two are: 1) the density and distribution of neutral hydrogen within the galaxy and 2) the number of ionizing photons produced. How the neutral medium is clumped significantly affects f_(esc). If there are some paths that photons follow out of the galaxy that do not intercept a clump, f_(esc) is greater than the case with no clumps, with clumps of higher density causing a greater f_(esc). If all paths intersect at least one clump, will drop below the no-clump case, and increasing the density of the clump will decrease f_(esc). Populations of stars with larger numbers of ionizing photons, such as metal-free or more massive stars, or disks with a high star formation efficiency increase f_(esc) because the angle from which photons can escape the disk is increased, allowing more to escape. f_(esc) also decreases for halos formed at higher redshifts because they are more dense, if there is no change in stellar population over redshilt. We also find that the mass of the galaxy does not affect f_(esc), as long as the star fbrmation efficiency is constant.