Density and temperature of cosmic-web filaments on scales of tens of megaparsecs

Abstract: We studied physical properties of matter in 24,544 filaments ranging from 30 to 100 Mpc in length, identified in the Sloan Digital Sky Survey (SDSS). We stacked the Comptonization y map produced by the Planck Collaboration around the filaments, excluding the resolved galaxy groups and clusters above a mass of ~3*10^13 Msun. We detected the thermal Sunyaev-Zel'dovich signal for the first time at a significance of 4.4 sigma in filamentary structures on such a large scale. We also stacked the Planck cosmic microwave background (CMB) lensing convergence map in the same manner and detected the lensing signal at a significance of 8.1 sigma. To estimate physical properties of the matter, we considered an isothermal cylindrical filament model with a density distribution following a beta-model (beta=2/3). Assuming that the gas distribution follows the dark matter distribution, we estimate that the central gas and matter overdensity and gas temperature are overdensity = (19.0 +27.3 -12.1) and temperature = (1.2 +- 0.4)*10^6 K, which results in a measured baryon fraction of (0.080 +0.116 -0.051) * Omega_b.