IGM Attenuation Bias for Lyman Continuum Detected Galaxies at z > 3.0

Wednesday September 9th 2020 @12pm, Zoom Colloquium
Dr Rob Bassett Swinburne University

Email: rbassett@swin.edu.au

Abstract

Understanding the sources responsible for driving reionization has been a major goal in astrophysics for many years. One critical measurement required is the ionizing (or Lyman continuum, LyC) escape fraction from observed galaxy samples. A major difficulty arises from the level of transmission of LyC through the intergalactic medium (IGM), an unknown (but essential) quantity in the calculation of LyC escape from individual sources. The typical method is to assume an average transmission value based on consideration of HI column density distribution functions, but is this appropriate? In general, observational surveys at high redshift are strongly biased towards the brightest objects as these are the easiest to detect. Given the fact that LyC emission is remarkably faint, we should expect to only detect those galaxies with the highest emergent LyC flux. This, in turn, suggests that detections of LyC in surveys will be biased towards IGM sightlines with higher than average transmission of ionizing photons. In this talk I discuss the quantification of this IGM transmission bias for LyC detections and explore the implications when considering the recovered LyC escape values from current surveys. Careful consideration of such biases will be critical in understanding how LyC escape depends on galaxy properties, which ultimately colours our understanding of how reionization proceeds.