Effect of the Metallicity on the X-ray Emission from the Warm-Hot Intergalactic Medium

TL;DR

This study uses hydrodynamic simulations to explore how metallicity affects the X-ray emission of the Warm-Hot Intergalactic Medium, revealing a strong dependence on metallicity models and consistency with current observations.

Contribution

It introduces a detailed analysis of metallicity's impact on WHIM X-ray emission using multiple models and compares predictions with observational constraints.

Findings

Emission strongly depends on metallicity model used.

Most emission originates from redshift z<1.2.

Predicted angular scale of emission is less than a few arcminutes.

Abstract

Hydrodynamic simulations predict that a significant fraction of the gas in the current Universe is in the form of high temperature, highly ionized plasma emitting and absorbing primarily in the soft X-ray and UV bands, dubbed the Warm-Hot Intergalactic Medium (WHIM). Its signature should be observable in red-shifted emission and absorption lines from highly ionized elements. To determine the expected WHIM emission in the soft X-ray band we used the output of a large scale hydrodynamic SPH simulation to generate images and spectra with angular resolution of 14'' and energy resolution of 1 eV. The current biggest limit of any hydrodynamic simulation in predicting the X-ray emission comes from metal diffusion. In our investigation, by using four different models for the WHIM metallicity we have found a strong dependence of the emission on the model used, with differences up to almost an order of magnitude. For each model we have investigated the redshift distribution and angular scale of the emission, confirming that most photons come from redshift z<1.2 and that the emission has a typical angular scale of less than a few arcminutes. We also compared our simulations with the few currently available observations and found that, within the variation of the metallicity models, our predictions are in good agreement with current constraints on the WHIM emission, and at this time the weak experimental constraints on the WHIM emission are not sufficient to exclude any of the models used.