Distinguishing the Nature of Dark Matter by Mapping Cosmic Filaments from Lyman-Alpha Emission.

The standard lambda cold dark matter cosmological model predicts that cosmic filaments are highly clumpy, whereas warm dark matter-invoked to address small-scale challenges in the lambda cold dark matter model-produces filaments that are noticeably smoother and less structured. In this Letter, we investigate the potential of Lyman-alpha emission to trace cosmic filaments at redshifts z=2.5 and z=4, and assess their potential for constraining the nature of dark matter. Our analysis shows that Lyman-alpha filaments provide a promising observational probe of dark matter: at z=4, differences in filament smoothness and surface brightness serve as distinctive signatures between models. Looking ahead, the upcoming generation of 30-m class telescopes will be critical for enabling these measurements, offering a compelling opportunity to distinguish the nature of dark matter by mapping the structure of cosmic filaments.