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

TL;DR

This work probes whether Lyα-emitting cosmic filaments can distinguish between cold and warm dark matter by comparing two zoom-in simulations of a Milky Way–like halo in CDM and a 1.5 keV warm relic, analyzing Lyα surface brightness and filament morphology at $z=4$ and $z=2.5$. Lyα emission is modeled from recombination and collisional excitation with self-shielding corrections, projected into 2D maps, and the observational feasibility is assessed with current and upcoming integral field spectrographs. The authors find that at $z=4$ WDM filaments are smoother and brighter than CDM ones, providing a distinctive signal, whereas by $z=2.5$ clumpiness reduces the contrast, highlighting a redshift dependence in detectability. They argue that next-generation $30$-meter class telescopes equipped with wide-field IFS can leverage these differences to constrain the nature of dark matter, complementing other probes like the Lyα forest and gravitational lensing.

Abstract

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

Figures (4)

• Figure 1: Maps of HI column density (top) and gas temperature (bottom) in WDM simulation. The left and right column show results at redshifts $z=4$ and $2.5$, respectively. The white circle marks the most massive halo at the center of the zoom-in region. Each panel spans 5.1 $\mathrm{cMpc}$.
• Figure 2: Same as Fig. \ref{['fig:temp and HI in wdm']}, but for CDM version.
• Figure 3: Difference in Ly$\alpha$ surface brightness between warm and cold dark matter simulations at redshifts $z=2.5$ and $4$. The white box represents the field-of-view of MUSE.
• Figure 4: Mock Ly$\alpha$ surface brightness maps at redshift $z=4$ for warm (left) and cold (right) dark matter. Rows correspond to the expected observational performance of different telescopes.