$X+y$: insights on gas thermodynamics from the combination of X-ray and thermal Sunyaev-Zel'dovich data cross-correlated with cosmic shear

We measure the cross-correlation between cosmic shear from the third-year release of the Dark Energy Survey, thermal Sunyaev-Zel’dovich (tSZ) maps from Planck, and X-ray maps from ROSAT. We investigate the possibility of developing a physical model able to jointly describe both measurements, simultaneously constraining the spatial distribution and thermodynamic properties of hot gas. We find that a relatively simple model is able to describe both sets of measurements and to make reasonably accurate predictions for other observables (the tSZ auto-correlation, its cross-correlation with X-rays, and tomographic measurements of the bias-weighted mean gas pressure). We show, however, that contamination from X-ray AGN, as well as the impact of non-thermal pressure support, must be incorporated in order to fully resolve tensions in parameter space between different data combinations. We obtain simultaneous constraints on the mass scale at which half of the gas content has been expelled from the halo, $\mathrm{log}{10}(M_c)=14.83^{+0.16}{-0.23}$, on the polytropic index of the gas, $Γ=1.144^{+0.016}{-0.013}$, and on the ratio of the central gas temperature to the virial temperature $α_T=1.30^{+0.15}{-0.28}$.

💡 Research Summary

This paper presents a joint analysis of three large‑scale‑structure observables: cosmic shear from the third‑year Dark Energy Survey (DES Y3), thermal Sunyaev‑Zel’dovich (tSZ) maps from Planck, and soft X‑ray maps from ROSAT. By measuring the cross‑correlations between shear‑tSZ (Cℓγy) and shear‑X‑ray (CℓγX) the authors aim to constrain the spatial distribution and thermodynamic state of hot gas in dark‑matter halos, while simultaneously testing a physically motivated halo‑model description of the gas.

Model framework
The authors adopt a “hydro‑dynamical halo model” that splits the total matter density into four components: cold dark matter (CDM), stars, bound (virialised) gas, and ejected gas. Each component is characterised by a mass‑fraction f x(M) and a radial profile g x(r|M). CDM follows a truncated NFW profile; stars are treated as a central point mass with a log‑normal stellar‑mass fraction; bound gas is described by a polytropic equation of state P∝ρΓ in hydrostatic equilibrium within an NFW potential, yielding a density profile g b(r)∝