Quantify the fraction of stacked SZ Compton-y attributable to X-ray–emitting WHIM in filaments

Determine the fraction of the total stacked Sunyaev–Zeldovich Compton-y signal measured at the spines of cosmic filaments that is contributed specifically by the X-ray–emitting warm–hot intergalactic medium phases detected by eROSITA, in order to robustly constrain joint X-ray–SZ models of filament baryon density contrast and volume filling factor without relying on ad hoc priors.

Background

To infer the baryon density contrast and volume filling factor of the X-ray–emitting warm–hot intergalactic medium (WHIM) in cosmic filaments, the authors jointly model stacked eROSITA X-ray profiles with an SZ-based constraint on the Compton-y signal at the filament spine. Because broadband X-ray emission traces only the hottest and densest WHIM phases, while SZ signals integrate thermal electron pressure from multiple gas phases along the line of sight, the relative contribution of the X-ray–bright WHIM to the total SZ signal is critical for breaking parameter degeneracies.

In the absence of a measured fraction, the analysis adopts an upper limit based on previous stacked SZ measurements and introduces a Gaussian prior on the central Compton-y. However, the precise fraction of the SZ signal that arises from the X-ray–emitting gas remains unknown, directly impacting the robustness of the inferred density and volume fraction parameters. Establishing this fraction would enable a less assumption-dependent joint X-ray–SZ characterization of filament WHIM properties.