Evidence for efficient long-range AGN jet feedback from the low redshift Lyman-$\alpha$ forest

Active galactic nuclei (AGN) feedback models are generally calibrated to reproduce galaxy observables such as the stellar mass function and the bimodality in galaxy colors. We use variations of the AGN feedback implementations in the IllustrisTNG (TNG) and Simba cosmological hydrodynamic simulations to show that the low redshift Lyman-$\alpha$ forest provides powerful independent constraints on the impact of AGN feedback. We show that TNG over predicts the number density of absorbers at column densities $N_{\rm HI} < 10^{14}$ cm$^{-2}$ compared to data from the Cosmic Origins Spectrograph (in agreement with previous work), and we demonstrate explicitly that its kinetic feedback mode, which is primarily responsible for galaxy quenching, has a negligible impact on the column density distribution (CDD) of absorbers. In contrast, we show that the fiducial Simba model including AGN jet feedback provides an excellent fit to the observed CDD of the $z = 0.1$ Lyman-$\alpha$ forest across five orders of magnitude in column density. When removing the jet feedback mode in Simba we recover similar results as TNG, reminiscent of the ionizing "photon underproduction crisis", a problem which arose from simulations lacking efficient heating/ionization of intergalactic medium (IGM) gas on large scales. AGN jets in Simba are high speed, collimated, weakly-interacting with the interstellar medium (via brief hydrodynamic decoupling) and heated to the halo virial temperature. Collectively these properties result in stronger long-range impacts on the IGM when compared to TNG kinetic feedback, which drives isotropic winds with lower velocities at the galactic radius. Our results suggest that the low redshift Lyman-$\alpha$ forest provides plausible evidence for long-range AGN jet feedback.