Constraints on the dark matter-baryon interaction cross section from galaxy cluster thermodynamics

TL;DR

This paper develops a thermodynamics-based constraint on velocity-independent DM–baryon cross sections using the intracluster medium of galaxy clusters. By constructing a heating–cooling balance that includes AGN feedback, bremsstrahlung cooling, and DM–baryon heat exchange, and enforcing approximate thermal equilibrium, the authors bound the DM–baryon cooling rate as a function of DM mass. Applying the model to a curated sample of REFLEX/MCXC clusters with ACT SZ masses, they derive a 95% upper bound of $\sigma_0 < 9.3\times10^{-28}\ \mathrm{cm^2}$ for $m_\chi$ in $[10^{-4}, 10^{-1}]\ \mathrm{GeV}$, with stronger bounds for fractional IDM scenarios ($f_\chi=0.1$ or $0.01$). The results are competitive with, and complementary to, existing constraints from the CMB and Milky Way satellites, and demonstrate the potential of using SZ-informed cluster thermodynamics to tighten DM–baryon interaction limits in the near future.

Abstract

Dark matter (DM) models with a non-zero DM-baryon interaction cross section imply energy transfer between DM and baryons. We present a new method of constraining the DM-baryon interaction cross section and DM particle mass for velocity-independent interactions using the thermodynamics of galaxy clusters. If the baryonic gas in these clusters is in thermodynamic equilibrium and DM cools baryons, this cooling rate is limited by the net heating rate of other mechanisms in the cluster. We use the REFLEX clusters from the Meta-Catalogue of X-ray detected Clusters of Galaxies (MCXC) with mass estimates from the Atacama Cosmology Telescope (ACT) catalog of Sunyaev-Zel'dovich (SZ) selected galaxy clusters. This yields 95% upper bounds on the DM-proton interaction cross section for velocity-independent interactions of $σ_0\leq9.3\times10^{-28} \mathrm{~cm^2}$ for DM masses, $m_χ= 10^{-4} - 10^{-1}$ GeV. These constraints are within an order of magnitude of the best constraints derived in this mass range, and serve as a complementary, independent constraint. We also apply this model to the fractional interacting DM scenario, where only 10% and 1% of the DM is interacting. Unlike other methods, this constraint scales linearly with this fraction. This yields 95% upper bounds of $σ_0\leq1.1\times10^{-26} \mathrm{~cm^2}$ and $σ_0\leq8.2\times10^{-26} \mathrm{~cm^2}$, which are the strongest existing constraints for this scenario. This paper serves as a proof of concept. Upcoming SZ measurements will provide temperature profiles for galaxy clusters. Combining these measurements with more complex thermodynamic models could lead to more robust constraints.

Figures (2)

• Figure 1: Left: The ratio of 2 times the thermal energy of the ICM to the absolute value of the potential energy for 49 clusters in the REFLEX dataset as a function of redshift. The plotted clusters are all within 2$\sigma$ of the solid black line, which indicates virialization. The reduced chi-squared value $\chi^2_{red}=0.24$ suggests a good fit, indicating the data points align with the virial equilibrium model. The error bars shown are propagated from the 68% confidence intervals for $M_{500}$ and $L_{500}$, described in more detail in section \ref{['sec:data']}.Right: The heating rate due to AGN feedback of the ICM in the same REFLEX clusters based on the ref. Iqbal2023 effervescent heating model, vs the cooling rate from bremsstrahlung given in ref. Rybicki1979. The black line represents the line where the AGN heating rate and the radiative cooling rate due to bremsstrahlung are equal in magnitude. The relatively high $\chi^2_{red}=6.83$ and deviation from the black line indicates this model may not fully capture all heating and cooling mechanisms in clusters (see section \ref{['sec: discussion']} for more information).
• Figure 2: Left: Upper bounds on the DM-proton velocity independent scattering cross section $\sigma_0$ as a function of $m_\chi$. The blue shaded region indicates the region excluded by this work, which is compared with constraints from MW satellites Maamari2021 (in gray with no hatching) and the CMB Gluscevic2018 (in gray with crossed diagonal lines hatching). The region above the blue shaded region represents the area excluded from the MCMC prior based on the interaction rate limit outlined in the end of section \ref{['sec:modeling']}. Within this region, the interaction rate is high enough that the DM and baryon temperatures can no longer be considered constant, and therefore this method cannot provide constraints within that region. We report orders of magnitude improvement over the ref. Gluscevic2018 constraints, and comparable bounds to the ref. Maamari2021 constraints within this mass range. Right: 95% upper bounds on the DM-proton velocity independent scattering cross section for a 2-component scenario where part of the DM is non-interacting. $f_\chi$ represents the fraction of DM that has interactions with protons. The shaded regions represent the regions excluded by this work for different $f_\chi$. The strength of this constraint scales linearly with $f_\chi$.