Probing the parameters of the intergalactic medium using quasars

Abstract

We continue our series of papers on intergalactic medium (IGM) tracers using quasi-stellar objects (QSOs), having examined gamma-ray bursts (GRBs) and blazars in earlier studies. We have estimated the IGM properties of hydrogen column density ($\mathit {N}\small {\rm hxigm}$), temperature and metallicity using XMM-Newton QSO spectra over a large redshift range, with a collisional ionisation equilibrium (CIE) model for the ionised plasma. The $\mathit {N}\small {\rm hxigm}$ parameter results were robust with respect to intrinsic power laws, spectral counts, reflection hump and soft excess features. There is scope for a luminosity bias given both luminosity and $\mathit {N}\small {\rm hxigm}$ scale with redshift, but we find this unlikely given the consistent IGM parameter results across the other tracer types reviewed. The impact of intervening high column density absorbers was found to be minimal. The $\mathit {N}\small {\rm hxigm}$ from the QSO sample scales as (1 + z)1.5 ± 0.2. The mean hydrogen density at z = 0 is n0 = (2.8 ± 0.3) × 10−7 cm−3, the mean IGM temperature over the full redshift range is log(T/K) =6.5 ± 0.1, and the mean metallicity is [X/H] = −1.3 ± 0.1(Z ∼ 0.05). Aggregating with our previous GRB and blazar tracers, we conclude that we have provided evidence of the IGM contributing substantially and consistently to the total X-ray absorption seen in the spectra. These results are based on the necessarily simplistic slab model used for the IGM, due to the inability of current X-ray data to constrain the IGM redshift distribution.

Probing the physical properties of the intergalactic medium using SRG/eROSITA spectra from blazars

“…One perspective postulates that the host source causes all the excess and evolution (Owens et al 1998;Galama & Wijers 2001;Stratta et al 2004;Campana et al 2006Campana et al , 2010Schady et al 2011;Watson et al 2013;Arcodia et al 2016;Buchner & Bauer 2017). Another perspective argues that the IGM contributes substantially to the absorption, and that it is therefore redshift related (Starling et al 2013;Campana et al 2015;Rahin & Behar 2019;Dalton & Morris 2020;Dalton et al 2021bDalton et al , 2022. Blazars are sources with negligible X-ray absorption along the line-of-sight (LOS) within the host galaxy.…”