The broadening of Lyman-alpha forest absorption lines

TL;DR

This paper develops an analytical model for the broadening of Lyman-alpha forest lines due to Doppler effects and Jeans smoothing, aiding in understanding the intergalactic medium's thermal state.

Contribution

It introduces a new analytical relation that accurately describes line broadening dependence on column density for narrow lines at z~3.

Findings

Model captures line-width dependence on column density for narrow lines

Broad lines indicate complex density structures not modeled by the relation

Enables new methods to characterize the intergalactic medium's thermal state

Abstract

We provide an analytical description of the line broadening of HI absorbers in the Lyman-alpha forest resulting from Doppler broadening and Jeans smoothing. We demonstrate that our relation captures the dependence of the line-width on column density for narrow lines in z~3 mock spectra remarkably well. Broad lines at a given column density arise when the underlying density structure is more complex, and such clustering is not captured by our model. Our understanding of the line broadening opens the way to a new method to characterise the thermal state of the intergalactic medium and to determine the sizes of the absorbing structures.