Panel a: symmetrically stacked Compton y-parameter maps for 1 million close pairs of CMASS galaxies. Panel b: modelled signal from the galaxy host haloes only. Panel c: residual between the stacked data and model. The indicated horizontal and vertical distance scales (r_∥ and r_⊥ respectively) are calibrated using the mean galaxy pair separation of 10.5 h⁻¹ Mpc. The mean projected angular separations are also shown for the horizontal axis. There is a bridge connecting the pairs of galaxies in the data (panel a) but not in the model (panel b), suggesting the presence of a filament in panel a, which is highlighted in panel c by a dashed box with plus signs indicating the positions of the galaxy pairs.