The Lyman-α forest is a key diagnostic for the state of diffuse baryons in the intergalactic medium (IGM) and for fundamental cosmological parameters. At high redshift (i.e., z ≥ 2) the Lyman-α forest is observed in optical wavelengths from ground-based observatories 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 (UVB) radiation. However, the low redshift (z~0.1) Lyman-α forest, observed from space-based UV instruments such as HST COS, has challenged the most advanced cosmological simulations. In this talk, I will show how active black hole (AGN) feedback can be at least as important (or more!) as the UVB for setting the amount and distribution of neutral gas in the low redshift IGM. The AGN feedback signatures appear in the neutral gas statistics beginning around z~1, thus possibly affecting 21-cm intensity mapping programs that target this redshift range (e.g., HIRAX). These findings herald a significant paradigm shift for cosmological simulations and observations that target the low redshift IGM and suggest that cosmological simulations should develop AGN feedback models with both galaxies and the IGM in mind.
https://go.illinois.edu/AstroColloquium
