Probing the warm dark matter mass with [C II] intensity mapping

TL;DR

This paper investigates how line-intensity mapping of [C II] emission can constrain the warm dark matter particle mass, providing forecasts for future surveys and analyzing the impact of survey parameters on the constraints.

Contribution

It develops a halo-model based formulation for the [C II] power spectrum incorporating luminosity function uncertainties and performs Bayesian forecasts for constraining WDM mass.

Findings

Current surveys can set lower limits on WDM mass around 0.58-1.10 keV.

Futuristic surveys could improve constraints up to 5.82 keV.

Increasing spectral resolution enhances sensitivity and tightens constraints.

Abstract

The nature of dark matter (DM) is still debated. While cold DM (CDM) is the standard paradigm, warm DM (WDM) may ease some small-scale tensions in the $\Lambda$CDM framework. Line-intensity mapping (LIM) offers a novel probe of DM properties. To explore the potential of LIM surveys in constraining the WDM particle mass ($m_\mathrm{WDM}$) by means of the [C II] power spectrum (PS), we provide forecasts for the Deep Spectroscopic Survey (DSS) at $z\simeq3.6$ and extend the analysis to larger sky coverage, higher sensitivity, and/or increased spectral resolution. We developed a formulation for the [C II] PS based on the halo-model approach, incorporating the uncertainty in the luminosity function (LF) through two alternative parameterisations. We performed a Bayesian analysis on mock data to derive constraints on $m_\mathrm{WDM}$. In a CDM universe, the DSS yields lower limits on $m_\mathrm{WDM}$, at a $95\%$ credibility level, of $1.10$ keV and $0.58$ keV when considering the optimistic and pessimistic LF ($\alpha = -1.1$), respectively. Ambitious surveys can improve these figures to $5.82$ keV and $1.90$ keV, and assuming a steeper faint-end slope ($\alpha = -1.9$) further boosts these limits. A fivefold increase in spectral resolution enhances sensitivity to the damping scale associated with redshift-space distortions, tightening the constraints on $m_\mathrm{WDM}$ by a factor of up to $\sim1.8$. Finally, Bayesian inference on mock data with $m_\mathrm{WDM}=3$ keV results in a well-constrained and unbiased posterior only in futuristic survey setups. Upcoming LIM surveys can provide meaningful limits on $m_\mathrm{WDM}$, although the negligible contribution from small haloes reduces the constraining power of the [C II] PS. Future progress will benefit from combining multiple redshifts and emission lines, opening the way to competitive constraints on the nature of DM.