2019MNRAS.483..223T

We search the Planck data for a thermal Sunyaev-Zel'dovich (tSZ) signal due to gas filaments between pairs of Luminous Red Galaxies (LRGs) taken from the Sloan Digital Sky Survey Data Release 12 (SDSS/DR12). We identify ∼260 000 LRG pairs in the DR12 catalogue that lie within 6-10 h^–1 Mpc of each other in tangential direction and within 6 h^–1 Mpc in radial direction. We stack pairs by rotating and scaling the angular positions of each LRG so they lie on a common reference frame, then we subtract a circularly symmetric halo from each member of the pair to search for a residual signal between the pair members. We find a statistically significant (5.3σ) signal between LRG pairs in the stacked data with a magnitude Δy = (1.31 ± 0.25) x 10^–8. The uncertainty is estimated from two Monte Carlo null tests which also establish the reliability of our analysis. Assuming a simple, isothermal, cylindrical filament model of electron overdensity with a radial density profile proportional to r_c/r (as determined from simulations), where r is the perpendicular distance from the cylinder axis and r_c is the core radius of the density profile, we constrain the product of overdensity and filament temperature to be δ_ c_ ×(T_ e_/10⁷^ K^) ×(r_ c_/0.5h^–1 Mpc) = 2.7 ±0.5. To our knowledge, this is the first detection of filamentary gas at overdensities typical of cosmological large-scale structure. We compare our result to the BAHAMAS suite of cosmological hydrodynamic simulations (McCarthy et al. 2017) and find a slightly lower, but marginally consistent Comptonization excess, Δy = (0.84 ± 0.24) x 10^–8.