ON THE CONTRIBUTION OF FLUORESCENCE TO LYα HALOS AROUND STAR-FORMING GALAXIES

Abstract

ABSTRACT We quantify the contribution of Ly α fluorescence to observed spatially extended Ly α halos around Ly α emitters at redshift z = 3.1. The key physical quantities that describe the fluorescent signal include (i) the distribution of cold gas in the circumgalactic medium (CGM); we explore simple analytic models and fitting functions to recent hydrodynamical simulations; and (ii) local variations in the ionizing background due to ionizing sources that cluster around the central galaxy. We account for clustering by boosting the observationally inferred volumetric production rate of ionizing photons, , by a factor of , in which quantifies the clustering of ionizing sources around the central galaxy. We compute by assigning an “effective” bias parameter to the ionizing sources. This novel approach allows us to quantify our ignorance of the population of ionizing sources in a simple parametrized form. We find a maximum enhancement in the local ionizing background in the range 50–200 at r ∼ 10 physical kpc. For spatially uncorrelated ionizing sources and fluorescing clouds we find that fluorescence can contribute up to ∼ 50%–60% of the observed spatially extended Ly α emission. We briefly discuss how future observations can shed light on the nature of Ly α halos around star-forming galaxies.