# Haro 11: Where is the Lyman continuum source?

## TL;DR

This study uses ionization-parameter mapping with Hubble imaging to identify the likely LyC escape source in Haro 11, finding it originates from a young, high-ionization region near Knot A, independent of Lyα emission.

## Contribution

The paper introduces a new continuum subtraction method and applies ionization-parameter mapping to spatially resolve LyC escape regions in Haro 11, clarifying the LyC source.

## Key findings

- No conclusive LyC escape from Knots B or C.
- High-ionization region extends from Knot A.
- Knot A is very young, possibly hosting massive stars.

## Abstract

Identifying the mechanism by which high energy Lyman continuum (LyC) photons escaped from early galaxies is one of the most pressing questions in cosmic evolution. Haro 11 is the best known local LyC leaking galaxy, providing an important opportunity to test our understanding of LyC escape. The observed LyC emission in this galaxy presumably originates from one of the three bright, photoionizing knots known as A, B, and C. It is known that Knot C has strong Ly$\alpha$ emission, and Knot B hosts an unusually bright ultraluminous X-ray source, which may be a low-luminosity AGN. To clarify the LyC source, we carry out ionization-parameter mapping (IPM) by obtaining narrow-band imaging from the Hubble Space Telescope WFC3 and ACS cameras to construct spatially resolved ratio maps of [OIII]/[OII] emission from the galaxy. IPM traces the ionization structure of the interstellar medium and allows us to identify optically thin regions. To optimize the continuum subtraction, we introduce a new method for determining the best continuum scale factor derived from the mode of the continuum-subtracted, image flux distribution. We find no conclusive evidence of LyC escape from Knots B or C, but instead, we identify a high-ionization region extending over at least 1 kpc from Knot A. Knot A shows evidence of an extremely young age ($\lesssim 1$ Myr), perhaps containing very massive stars ($>100$ M$_\odot$). It is weak in Ly$\alpha$, so if it is confirmed as the LyC source, our results imply that LyC emission may be independent of Ly$\alpha$ emission.