Orateur
Description
The X-ray spectrum of extragalactic sources, such as galaxy clusters, is affected by the photo-absorption of various components of the Galactic InterStellar Medium (ISM). The resulting spectral distortion contributes to the systematics of cluster temperature measurements. It essentially depends on the total (atomic+molecular) Galactic hydrogen density column, N_H, which remains challenging to map across the sky in the lack of a straightforward tracer of the molecular gas phase in the ISM. Combining data from the Planck HFI and HI4PI sky surveys, we investigate the mass fraction of molecular gas across the line of sight of CHEX-MATE galaxy clusters by looking for thermal dust emission excesses with respects to the neutral atomic hydrogen density column, N_HI. Consistent with earlier studies of the ISM based on IRAS and Planck data, we detect dust emission excesses along the line of sight of some members of the CHEX-MATE cluster catalogue mostly localised in dense ISM regions. We find that the CHEX-MATE cluster catalogue can be divided in 40 % of members located behind low N_HI regions where the molecular mass fraction is negligible, 40% of members located in intermediate N_HI regions where the molecular gas fraction would reach 10% on average, and the remaining 20% of members located in high N_HI regions that locally exhibits even higher molecular gas fractions. The cluster temperature shifts associated with molecular content of the ISM is about 1% or less for most CHEX-MATE clusters, but can exceed 5% in the highest N_HI regions.
