Rutgers University Astrophysics Colloquium

Lyman-alpha absorption lines are a key diagnostic for the state of diffuse baryons in the intergalactic medium (IGM) and for fundamental cosmological parameters. Light shining from distant active galaxies is absorbed by intergalactic hydrogen clouds, creating a “forest” of redshifted absorption lines. At high redshift (i.e., z > 2) the “Lyman-alpha forest” physics is well understood and has been used to constrain small-scale cosmic structure, the dark matter distribution, the IGM gas temperature, and the evolution of the ultraviolet ionizing background radiation. However, the low redshift (z~0.1) Lyman-alpha forest observations have challenged the most advanced cosmological simulations and defy physical arguments that work well at z>2, as the amount of neutral hydrogen predicted is far larger in simulations than what is observed. In this talk, I will show how including active black hole feedback can reconcile the amount of neutral gas by providing extra heating. These findings herald a significant paradigm shift for cosmological simulations and observations that target the low redshift IGM. I will also highlight the importance of intergalactic turbulence in this picture and provide some connections to other adjacent work on astrophysical turbulence at Rutgers.