Distinguishing the nature of dark matter by mapping cosmic filaments from Lyman-alpha emission

The standard $\mathrm{\Lambda }$CDM cosmological model predicts that cosmic filaments are highly clumpy, whereas warm dark matter – invoked to address small-scale challenges in $\mathrm{\Lambda }$CDM – produces filaments that are noticeably smoother and less structured. In this work, we investigate the potential of Lyman $\alpha$ (Ly$\alpha$) 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 Ly$\alpha$ 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-meter 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.