Lighting Up Reionization through a Multi-Line Perspective

The Epoch of Reionization (EoR) marks the final phase transition in our Universe, as the hydrogen in the intergalactic medium evolves from cold and neutral to hot and ionized. While current observations constrain its endpoint and duration, and JWST is pushing detections to higher redshifts, large uncertainties remain.

Line Intensity Mapping (LIM) offers a powerful complementary probe by capturing the cumulative emission from both bright and faint galaxies. Investigating its applications is especially timely with the recent launch of SPHEREx, the first mission to feature multi-line LIM among its primary science goals, and with the ground-based interferometers HERA and LOFAR increasing their sensitivity and already setting upper limits on the 21-cm power spectrum.

In this talk, I will discuss a novel approach to model this multi-line framework, and I will show how cross-correlations between star-forming lines and the 21-cm signal can reveal the physics of the EoR, transitioning from positive at early times to negative as ionized bubbles grow. Detecting it would offer a firm observational anchor for reionization, yielding unprecedented insights into early galaxy formation and the dawn of cosmic structure.