摘要：Observations of galaxies and galaxy clusters in the local universe can account for only ∼10% of the total baryon content. Cosmological simulations predict that the “missing baryons” are spread throughout filamentary structures in the cosmic web, forming a low-density gas with temperatures of 105−107K. We search for this warm-hot intergalactic medium (WHIM) by stacking thePlanckComptony-parameter map of the thermal Sunyaev-Zel’dovich (tSZ) effect for 1 002 334 pairs of CMASS galaxies from the Sloan Digital Sky Survey. We model the contribution from the galaxy halo pairs assuming spherical symmetry, finding a residual tSZ signal at the 2.9σlevel from a stacked filament of length 10.5 h−1Mpc with a Compton parameter magnitudey = (0.6 ± 0.2)×10−8. We consider possible sources of contamination and conclude that bound gas in haloes may contribute only up to 20% of the measured filamentary signal. To estimate the filament gas properties we measure the gravitational lensing signal for the same sample of galaxy pairs; in combination with the tSZ signal, this yields an inferred gas density ofρb = (5.5 ± 2.9) × ρ̄bwith a temperatureT = (2.7 ± 1.7) × 106K. This result is consistent with the predicted WHIM properties, and overall the filamentary gas can account for 11 ± 7% of the total baryon content of the Universe. We also see evidence that the gas filament extends beyond the galaxy pair. Averaging over this longer baseline boosts the significance of the tSZ signal and increases the associated baryon content to 28 ± 12% of the global value.
关键词：encosmology: observationslarge-scale structure of Universecosmic background radiationintergalactic medium
