Measurement of the small-scale structure of the intergalactic medium using close quasar pairs

Understand

The distribution of diffuse gas in the intergalactic medium (IGM) imprints a series of hydrogen absorption lines on the spectra of distant background quasars known as the Lyman-$\alpha$ forest.

• Cosmological hydrodynamical simulations predict that IGM density fluctuations are suppressed below a characteristic scale where thermal pressure balances gravity.
• We measured this pressure-smoothing scale by quantifying absorption correlations in a sample of close quasar pairs.
• We compared our measurements to hydrodynamical simulations, where pressure smoothing is determined by the integrated thermal history of the IGM.