The Effects of Active Galactic Nuclei Feedback on the Lyα Forest Flux Power Spectrum

Abstract We study the effects of active galactic nuclei (AGN) feedback on the Ly α forest 1D flux power spectrum (P1D). Using the Simba cosmological-hydrodynamic simulations, we examine the impact that adding different AGN feedback modes has on the predicted P1D. We find that, for Simba , the impact of AGN feedback is most dramatic at lower redshifts ( z < 1) and that AGN jet feedback plays the most significant role in altering the P1D. The effects of AGN feedback can be seen across a large range of wavenumbers (1.5 × 10 −3 < k < 10 −1 s km −1 ) changing the ionization state of hydrogen in the IGM through heating. AGN feedback can also alter the thermal evolution of the IGM and thermally broaden individual Ly α absorbers. For the Simba model, these effects become observable at z ≲ 1.0. At higher redshifts ( z > 2.0), AGN feedback has a 2% effect on the P1D for k < 5 × 10 −2 s km −1 and an 8% effect for k > 5 × 10 −2 s km −1 . We show that the small-scale effect is reduced when normalizing the simulation to the observed mean flux. On large scales, the effect of AGN feedback appears via a change in the IGM temperature and is thus unlikely to bias cosmological parameters. The strong AGN jets in the Simba simulation can reproduce the z > 2 Ly α forest. We stress that analyses comparing different AGN feedback models to future higher precision data will be necessary to determine the full extent of this effect.