The thermal Sunyaev-Zel'dovich Signature of Baryons in the Local Universe

Abstract

Using cosmological hydrodynamical simulations, we investigate the prospects of the thermal Sunyaev-Zel'dovich (tSZ) effect to detect the missing baryons in the local universe. We find that at least 80% of the tSZ luminosity is generated in collapsed structures, and that $\sim$ 70% of the remaining diffuse tSZ luminosity (i.e., $\sim 15$% of the total) comes from overdense regions with $\delta_{gas}>$10, such as filaments and superclusters. The gas present in slightly overdense and underdense regions with $\delta_{gas} < 10$, despite making up 50% of the total baryon budget, leaves very little tSZ signature: it gives rise to only $\sim$ 5% of the total tSZ luminosity. Thus, future Cosmic Microwave Background (CMB) observations will be sensitive to, at best, one half of the missing baryons, improving the current observational status, but still leaving one half unobserved. Since most of the tSZ is generated in haloes, we find a tight correlation between gas pressure and galaxy number density. This allows us to predict the CMB Comptonization from existing galaxy surveys and to forecast the tSZ effect from the local structures probed by the Two Micron All Sky Survey (2MASS) galaxy catalog.