Measuring the properties of reionised bubbles with resolved Lyman alpha spectra

Understand

Identifying and characterising reionised bubbles enables us to track both their size distribution, which depends on the primary ionising sources, and the relationship between reionisation and galaxy evolution.

• We demonstrate that spectrally resolved $z\gtrsim6$ Lyman-alpha (Ly$\alpha$) emission can constrain properties of reionised regions.
• Specifically, the distant from a source to a neutral region sets the minimum observable Ly$\alpha$ velocity offset from systemic.
• Detection of flux on the blue side of the Ly$\alpha$ resonance implies the source resides in a large, sufficiently ionised region that photons can escape without significant resonant absorption, and thus constrains both the sizes of and the residual neutral fractions within ionised bubbles.