Jet feedback and the photon underproduction crisis in simba

ABSTRACT We examine the impact of black hole jet feedback on the properties of the low-redshift intergalactic medium (IGM) in the simba simulation, with a focus on the Lyα forest mean flux decrement DA. Without jet feedback, we confirm the photon underproduction crisis (PUC) in which ΓH i at z = 0 must be increased by 6 times over the Haardt at higher redshifts simba reproduces the observed DA with no adjustment, with or without jets. The main impact of jet feedback is to lower the cosmic baryon fraction in the diffuse IGM from 39 per cent to 16 per cent at z = 0, while increasing the warm-hot intergalactic medium (WHIM) baryon fraction from 30 per cent to 70 per cent; the lowering of the diffuse IGM content directly translates into a lowering of DA by a similar factor. Comparing to the older mufasa simulation that employs different quenching feedback but is otherwise similar to simba, mufasa matches DA less well than simba, suggesting that low-redshift measurements of DA and ΓH i could provide constraints on feedback mechanisms. Our results suggest that widespread IGM heating at late times is a plausible solution to the PUC, and that simba’s jet active galactic nucleus feedback model, included to quench massive galaxies, approximately yields this required heating.