X-ray emission from cosmic web filaments in SRG/eROSITA data

Abstract

Using the publicly available eROSITA Final Equatorial Depth Survey (eFEDS) data, we detected the stacked X-ray emissions at the position of 463 filaments at a significance of 3.8σ based on the combination of all energy bands. In parallel, we found that the probability of the measurement under the null hypothesis is ∼0.0017. The filaments were identified with galaxies in the Sloan Digital Sky Survey survey, ranging from 30 Mpc to 100 Mpc in length at 0.2 < z < 0.6. The stacking of the filaments was performed with the eFEDS X-ray count-rate maps in the energy range between 0.4 and 2.3 keV after masking the resolved galaxy groups and clusters and the identified X-ray point sources from the ROSAT, Chandra, XMM-Newton, and eROSITA observations. In addition, diffuse X-ray foreground and background emissions or any residual contribution were removed by subtracting the signal in the region between 10 and 20 Mpc from the filament spines. For the stacked signal, we performed an X-ray spectral analysis, which indicated that the signal is associated with a thermal emission. According to a model with the astrophysical plasma emission code for the plasma emission and with a β-model gas distribution with β = 2/3, the detected X-ray signal can be interpreted as emission from hot gas in the filaments with an average gas temperature of 1.0−0.2+0.3 keV and a gas overdensity of 21 ± 5 at the center of the filaments.