A search for warm/hot gas filaments between pairs of SDSS Luminous Red Galaxies

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 similar to 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 (5.3 sigma) signal between LRG pairs in the stacked data with a magnitude Delta y = (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 delta(c) x (T-e/10(7) K) x (r(c)/0.5 h(-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, Delta y = (0.84 +/- 0.24) x 10(-8).