Role of ionizing background on the non-thermal broadening inferred for the aligned absorbers

TL;DR

This study uses cosmological simulations to investigate how the ionizing background influences the non-thermal broadening of aligned intergalactic absorbers, revealing complexities in interpreting turbulence and temperature from line widths.

Contribution

It demonstrates that non-thermal broadening is significantly affected by feedback and UV background, challenging its use as a turbulence indicator and proposing combined analysis for better constraints.

Findings

Non-thermal broadening is affected by feedback and UV background.

Inferred temperatures correlate with kinetic temperatures but with large scatter.

Aligned absorber properties can constrain simulation parameters.

Abstract

Using cosmological hydrodynamical simulations at $z\sim0.5$, we measure the thermal ($b_{t}$) and non-thermal ($b_{nt}$) contribution to the line broadening for the intergalactic absorbers having \OVI\ and \HI\ absorption well aligned in the velocity space. We find that the inferred temperature based on $b_{t}$ correlates strongly with the optical depth-weighted kinetic temperature of the absorbing gas, albeit with a large scatter. We show this scatter comes from the spread in the kinetic temperature of the gas contributing to the absorption and hence depends on the feedback processes and the ionizing UV background (UVB) used in the simulations. We show the distribution of $b_{nt}$ is also affected by both feedback processes and the ionizing UVB. Therefore, $b_{nt}$ derived using aligned absorbers may not be a good probe of sub-grid turbulence. Therefore, $b_{nt}$ derived using aligned absorbers may not be a good discriminator between the effect of microscopic turbulence and UVB. Instead, the distribution of $b_{t}$ and $b_{nt}$ together with the frequency of occurrence of the aligned absorbers can be used to place additional constraints on the parameters of the simulation for a given assumed UVB.