The Sunburst Arc (z~2.37) is the brightest lensed galaxy identified to date with R~17.8mag. Due to a foreground galaxy cluster at z~0.44, the light from the Sunburst galaxy is bent around the cluster. This is what causes the galaxy light to be shaped into 4 separate arcs. Because of its brightness, we can measure its ionizing continuum and perform intergalactic medium tomography.
The Sunburst Arc is a confirmed Lyman continuum leaker with a single leaking HII region. Since it is at z~2.37, this means the galaxy must lack a large amount of dust, and the intergalactic medium along the line of sight must be relatively transparent. Using HST/WFC3 UVIS G280 slitless grism spectroscopy, I am directly measuring the escape fraction and comparing models to observations of the ionizing stellar continuum of a galaxy for the first time.
This is the HST/ACS F814W image of the Sunburst Arc. The galaxy is lensed into four arc segments by a foreground galaxy cluster. Incredibly, the leaking region of this galaxy has been imaged 12 times over all four arcs.
The image spectra probe slightly different lines of sight, but are close enough for tomographic mapping. Intervening foreground absorbers in the intergalactic medium are seen in the image spectra. Some of these absorbers are identified in multiple spectra, allowing me to constrain their physical sizes in 2D.