[Paper Review] Exploring delaying and heating effects on the 21-cm signature of fuzzy dark matter

Debanjan Sarkar, Jordan Flitter+1 more|arXiv (Cornell University)|Jan 10, 2022

Radio Astronomy Observations and Technology94 references22 citations

TL;DR

This paper models the 21-cm global signal in fuzzy dark matter (FDM) cosmologies using a modified 21cmvFAST code interfaced with CLASS, incorporating relative velocity, Lyman-Werner feedback, and Lyman-α/CMB heating effects. It finds that HERA can detect FDM particle masses up to 10⁻¹⁸ eV in optimistic foreground scenarios and down to 10⁻¹⁹ eV in realistic cases, despite delaying and heating mechanisms that weaken the signal.

ABSTRACT

In the fuzzy dark matter (FDM) model, dark matter is composed of ultra-light particles with a de Broglie wavelength of $\sim$kpc, above which it behaves like cold dark matter (CDM). Due to this, FDM suppresses the growth of structure on small scales, which delays the onset of the cosmic dawn (CD) and the subsequent epoch of reionization (EoR). This leaves potential signatures in the sky averaged 21-cm signal (global), as well as in the 21-cm fluctuations, which can be sought for with ongoing and future 21-cm global and intensity mapping experiments. To do so reliably, it is crucial to include effects such as the dark-matter/baryon relative velocity and Lyman-Werner star-formation feedback, which also act as delaying mechanisms, as well as CMB and \lya heating effects, which can significantly change the amplitude and timing of the signal, depending on the strength of X-ray heating sourced by the remnants of the first stars. Here we model the 21-cm signal in FDM cosmologies across CD and EoR using a modified version of the public code 21cmvFAST that accounts for all these additional effects, and is directly interfaced with the Boltzmann code CLASS so that degeneracies between cosmological and astrophysical parameters can be fully explored. We examine the prospects to distinguish between the CDM and FDM models and forecast joint astrophysical, cosmological and FDM parameter constraints achievable with intensity mapping experiments such as HERA and global signal experiments like EDGES. We find that HERA will be able to detect FDM particle masses up to $m_{ m FDM}\! \sim \!10^{-19}\,{ m eV}\!-\!10^{-18}\,{ m eV}$, depending on foreground assumptions, despite the mitigating effect of the delaying and heating mechanisms included in the analysis.

Motivation & Objective

• To investigate how fuzzy dark matter (FDM) alters the 21-cm global signal and fluctuations during cosmic dawn and reionization.
• To assess the impact of key astrophysical delaying mechanisms—relative velocity between baryons and dark matter, and Lyman-Werner feedback—on the 21-cm signal in FDM models.
• To evaluate the influence of Lyman-α and CMB heating on the signal amplitude and timing in both FDM and CDM scenarios.
• To forecast joint constraints on FDM, astrophysical, and cosmological parameters using upcoming 21-cm experiments like HERA and EDGES.
• To enable self-consistent, joint CMB and 21-cm parameter constraints through a direct interface between CLASS and 21cmvFAST.

Proposed method

• Modified the public 21cmvFAST code to include relative velocity effects, Lyman-Werner feedback, and Lyman-α and CMB heating mechanisms.
• Integrated the modified 21cmvFAST code with the CLASS Boltzmann code to ensure consistent cosmic evolution from before recombination.
• Calculated redshift-dependent relative-velocity effects and feedback parameters for each cosmological model to ensure accurate input to the 21-cm simulations.
• Used the modified code to generate 21-cm signal realizations across cosmic dawn and reionization in FDM cosmologies with varying particle masses.
• Performed joint parameter forecasts using simulated data from HERA and EDGES, accounting for foreground uncertainties.
• Explored degeneracies between cosmological, astrophysical, and FDM parameters through full-sky and global signal modeling.

Experimental results

Research questions

• RQ1 How do relative velocity and Lyman-Werner feedback affect the 21-cm signal in FDM cosmologies compared to CDM?
• RQ2 To what extent do Lyman-α and CMB heating mechanisms alter the amplitude and timing of the 21-cm signal in FDM models?
• RQ3 Can upcoming intensity mapping (HERA) and global signal (EDGES) experiments distinguish FDM from CDM, given these additional physical effects?
• RQ4 What are the joint constraints on FDM particle mass, X-ray heating efficiency, and other astrophysical parameters achievable with 21-cm data?
• RQ5 How do degeneracies between FDM, astrophysical, and cosmological parameters affect the detectability of FDM via 21-cm observations?

Key findings

• HERA will be able to detect FDM particle masses up to 10⁻¹⁸ eV in optimistic foreground scenarios.
• In more realistic foreground conditions, HERA’s sensitivity extends to FDM masses of approximately 10⁻¹⁹ eV.
• The inclusion of delaying and heating mechanisms reduces the detectable FDM mass range by roughly an order of magnitude compared to models without these effects.
• Lyman-α and CMB heating significantly alter the signal amplitude and timing, especially when X-ray heating is inefficient.
• The joint analysis of CMB and 21-cm data via the CLASS-21cmvFAST interface enables robust, self-consistent parameter constraints across cosmological and astrophysical parameters.
• Degeneracies between FDM, X-ray heating, and other astrophysical parameters remain significant but do not preclude detection of FDM with current and future 21-cm experiments.