Work

Pinpointing the cosmic web between massive galaxy clusters. I. The incidence of H i and O vi as WHIM tracers

Year: 2026

Type: article

Abstract: At redshift z<1, the current lambda cold dark matter (ΛCDM) paradigm predicts that sim40-50% of baryons ought to be located in the warm-hot intergalactic medium (WHIM) within cosmic web filaments. Characterizing the physical state of this dominant baryonic matter and its distribution is crucial for a complete picture of baryon evolution in the low-redshift Universe. However, directly observing the WHIM has been challenging due to its low density and high temperature and ionization state. Absorption line spectroscopy offers a promising route, particularly via analyses of broad łya absorbers (BLAs; Doppler parameter b absorbers. ̨ms) and O VI This work is focused on probing the signatures of the WHIM by analyzing the incidence rate of these tracers in and around putative cosmic web filaments connecting massive galaxy clusters. We employed far-ultraviolet (FUV) absorption spectroscopy acquired with the HST/COS along ten quasi-stellar object (QSO) sightlines at z<1 selected based on their proximity, in terms of the projected distance at a low velocity separation, to cluster pairs. We focused our analysis on absorption features of WHIM tracers (BLAs and ) and cold gas tracers (narrow łya absorbers, or NLAs; b<40 ̨ms), used as control samples for the temperature. O VI We measured an excess in the incidence rates of total , NLAs, BLAs, and within a rest-frame of Δ v= are approximately twice those of NLAs. Additionally, the covering fraction for BLAs and appears to be larger (by sim1.7 and sim1.8 times, respectively) than for a random (field) control sample of the environment, whereas the covering fraction for NLAs is consistent with the random expectation. H I O VI ̨ms and an impact parameter of Δ dłeq3 Mpc relative to the field expectation, finding that the excesses of BLAs and O VI O VI The greater relative excess of WHIM tracers compared to cold gas tracers in the vicinity of independent cluster pairs indicates the prevalence of warm-hot gas in these environments, representing a potential signature of WHIM detection in intercluster filaments.

Source: Astronomy and Astrophysics

DOI: 10.1051/0004-6361/202660539