Haro 11: Where is the Lyman Continuum Source?

Haro 11 is the best known source of Lyman continuum (LyC) emission in the local universe and is thought to be an analog of the early galaxies that drove cosmic reionization. The source of LyC emission within Haro 11 has not yet been identified, since the LyC detection is unresolved. To map the optically thin regions in this galaxy, we apply our technique of ionization parameter mapping, which uses continuum-subtracted, HST WFC3 and ACS narrowband images of [O III] and [O II] emission to construct ratio maps. These allow us to identify regions of the galaxy that are likely to be optically thin. Due to the importance of continuum subtraction for this technique, we also develop a new method for scaling the continuum images based on the mode of the pixel distribution. We find that a region extending from Haro 11 Knot A appears to be optically thin. Other regions of the galaxy have also been suggested as potential LyC sources, based on the presence of a ULX (Knot B) and Ly-alpha emission (Knot C). Our work now adds Knot A as a third candidate LyC source in this complex merger system. (This work was supported by NASA grant HST-GO-13702)