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

TL;DR

This study reports the first detection of X-ray emission from cosmic web filaments using eROSITA data, revealing hot gas with specific temperature and density properties, thus providing insights into the large-scale structure of the universe.

Contribution

First detection of X-ray emission from cosmic web filaments with detailed spectral analysis using eROSITA data, confirming the presence of hot gas in these structures.

Findings

Detected X-ray emission at 3.8 sigma significance from 463 filaments

Estimated filament gas temperature of approximately 1 keV

Measured gas overdensity of about 21 in the filaments

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 3.8 sigma 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 - 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 - 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 beta-model gas distribution with beta=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 (+0.3 -0.2) keV and a gas overdensity of 21 +- 5 at the center of the filaments.