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

## TL;DR

This study measures the small-scale structure of the intergalactic medium by analyzing absorption correlations in close quasar pairs, confirming models of thermal pressure effects consistent with cosmic reionization.

## Contribution

It provides the first observational measurement of the pressure-smoothing scale in the IGM using close quasar pairs, linking it to the thermal history of the universe.

## Key findings

- Pressure-smoothing scale measured aligns with hydrodynamical simulations.
- Results support standard photoionization heating models.
- Findings are consistent with the thermal history of the IGM.

## Abstract

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. Our findings are consistent with standard models for photoionization heating by the ultraviolet radiation backgrounds that reionized the universe.