Led by Dr. Xiaoyuan Zhang, a postdoctoral fellow at the Max Planck Institute for Extraterrestrial Physics (MPE), the team of scientists revealed the existence of high-temperature, high-density regions of the WHIM by utilizing data from the eROSITA All-Sky Survey (eRASS). Over the course of two years, eROSITA, a powerful X-ray telescope aboard the Spektr-RG spacecraft, observed weak X-ray emission from the WHIM. To amplify these faint signals, the researchers employed a technique known as stacking, analyzing X-ray data at the locations of more than 7,000 cosmic filaments identified through the optical Sloan Digital Sky Survey (SDSS).
Due to its extremely low density (10 particles per cubic meter on average), the WHIM is notoriously difficult to observe. "Numerous studies have attempted to detect the WHIM using X-ray absorption, emission through X-rays, and the Sunyaev-Zeldovich effect. While some have yielded modestly positive results, they are often questioned due to potential contamination and systematic uncertainties. Now, with the eROSITA All-Sky Survey providing the deepest all-sky X-ray data, we have a unique opportunity to detect WHIM X-ray emission associated with large-scale cosmic structure." remarks Esra Bulbul, who is leading the clusters and cosmology group at the Max Planck Institute for Extraterrestrial Physics (MPE).
Tracing Cosmic Filaments
“Surprisingly, we had a strong X-ray detection (9σ) of the cosmic web. This was not the end of the story. We also needed to carefully model the contamination from the undetected galactic sources, which was the key to disclosing how much of our signal is from the WHIM.” said Xiaoyuan Zhang, the study's leading author. The study introduces an innovative method for estimating contamination from unmasked X-ray halos, active galactic nuclei, and X-ray binaries associated with filament galaxies. The analysis revealed an approximate 40% contamination fraction, indicating that around 60% of the detected signal may originate from the WHIM, with a detection significance of 5.4σ.
The team looked deeper into the properties of the recently detected WHIM, which allows them to gather critical insights into its nature. Their findings of the state-of-the-art numerical simulation indicate that the observed X-ray signal likely originates from WHIM regions with temperatures in the range of several million Kelvin and densities of approximately 100 particles per cubic meter.
Next-Generation Galaxy Surveys
Andrea Merloni, Principal Investigator of the eROSITA project at MPE, ventures a look into the future: “Over the next few years, new large-scale spectroscopic galaxy surveys such as DESI and 4MOST will provide larger, more detailed galaxy and filament maps. The much larger overlap of these surveys with the eROSITA all-sky data will ensure a more refined analysis of the stacked X-ray data and bring to light new pieces of information on the WHIM physical state”.
Contact:
Dr. Xiaoyuan Zhang
Postdoc Highenergy Group
tel:+49 89 30000-3807
xzhang@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics
Dr. Esra Bulbul
Head of galaxy clusters group
tel:+49 89 30000-3502
ebulbul@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics
Nicola Malavasi
Marie Sklodowska-Curie EU Research Fellow High-Energy Group
tel:+49 89 30000-3040
malavasi@mpe.mpg.de
Max Planck Institute for Extraterrestrial Physics
Original Publication
Zhang, X.; Bulbul, E.; Malavasi, N.; Ghirardini, V. ; et al.
The SRG/eROSITA all-sky survey. X-ray emission from the warm-hot phase gas in long cosmic filaments.
A&A, 691, A234 (2024)
DOI
Further Information
ERC Project DarkQuest
Webpages of the ERC funded project led by Esra Bulbul
Cosmic dance of the ‘Space Clover’
April 30, 2024