eROSITA X-ray sky survey measurements show consistency with the cosmic microwave background

The evaluation of how galaxy clusters, the most important objects within the universe, evolve over cosmic time has yielded exact measurements of the total matter content material and its clumpiness, report scientists of the German eROSITA consortium, led by the Max Planck Institute for Extraterrestrial Physics and with participation of the College of Bonn.

The outcomes affirm the usual cosmological mannequin and alleviate the so-called S8 stress, whereas on the similar time providing insights into the elusive neutrinos’ mass. The evaluation relies on one of many largest catalogues of galaxy clusters and superclusters. An vital pillar within the evaluation is the “weighing” of the found galaxy clusters, for which the College of Bonn was a significant contributor.

eROSITA is an X-ray space telescope onboard the Spectrum-RG satellite, launched in July 2019. Two weeks in the past, the German eROSITA consortium released its data from the primary all-sky survey. The survey’s main purpose is to higher perceive cosmology by way of the measurement of the expansion over cosmic time of clusters of galaxies, a number of the largest buildings within the universe.

Tracing the evolution of clusters by way of the X-rays emitted by scorching fuel as detected by eROSITA mixed with strong mass measurements of those clusters via weak gravitational lensing, exact and accurate measurements of each the total quantity of matter density within the universe and its clumpiness have been made. Whereas previous clumpiness measurements utilizing totally different strategies, particularly the cosmic microwave background (CMB) and the so-called Cosmic Shear appeared inconsistent with one another, the eROSITA measurements now present consistency with the CMB.

“eROSITA has now established cluster evolution measurement as a instrument for precision cosmology,” mentioned Dr. Esra Bulbul (MPE), the lead scientist for eROSITA’s clusters and cosmology crew who delivered the groundbreaking outcomes. “The cosmological parameters that we measure from galaxy clusters are in step with state-of-the-art CMB exhibiting that the identical cosmological mannequin holds from quickly after the Huge Bang to right this moment.”

In response to the usual cosmological mannequin, known as the Lambda Chilly Darkish Matter (ΛCDM) mannequin, the toddler universe was a particularly scorching, dense sea of photons and particles. Over the course of cosmic time, tiny density variations grew into the big galaxies and galaxy clusters we are able to see right this moment. The eROSITA cluster observations present that matter of all types (seen and darkish) includes 29% of the total mass/vitality funds of the universe, in glorious settlement with the values obtained from measurements of the CMB, which was emitted when the universe first grew to become clear.

In addition to measuring the total matter density within the universe, eROSITA has additionally measured the clumpiness of the matter distribution, described by way of the so-called S8 parameter. An vital growth in cosmology lately has been the so-called “S8 stress.” This stress arises as a result of CMB experiments measure the next S8 worth than, e.g., Cosmic Shear surveys.

New physics is implied except this stress could be resolved, and eROSITA has carried out simply that. “eROSITA tells us that the universe behaved as anticipated all through cosmic historical past,” says Dr. Vittorio Ghirardini, the postdoctoral researcher at MPE who led the cosmology study posted to the arXiv preprint server. “There is no stress with the CMB—perhaps the cosmologists can chill out a bit now.”

The most important objects within the universe additionally carry details about the smallest particles: neutrinos. These light-weight particles are practically unimaginable to detect. From the abundance of the most important dark matter haloes within the universe the eROSITA crew have obtained tight constraints on the mass of the lightest identified particles. The eROSITA cluster outcomes yield the tightest mixed neutrino mass measurement to this point from any observational cosmology probe.

An vital part of the evaluation are weak gravitational lensing measurements. This impact describes coherent distortions which are imprinted onto the noticed shapes of distant galaxies when their mild rays cross via the gravitational area of foreground buildings. Whereas Cosmic Shear research probe the impact alongside random instructions, it can be measured within the neighborhood of galaxy clusters to estimate their plenty.

The eROSITA crew has performed such measurements incorporating information from three present weak gravitational lensing surveys, the Darkish Power Survey (DES), the Hyper Suprime Cam Survey (HSC), and the Kilo-Diploma Survey (KiDS). These measurements calibrate the relation between the eROSITA X-ray sign and cluster mass, thereby enabling the comparability to cosmological mannequin predictions.

“I am pleased with the weak lensing crew that did a wonderful job in offering the evaluation from all three main weak lensing surveys for the eROSITA cluster mass calibration, which enabled these cosmology constraints; one thing that has by no means been achieved earlier than” says Prof. Dr. Thomas Reiprich from the Argelander Institute for Astronomy (AIfA) on the College of Bonn, who led the weak lensing mass calibration work package deal inside the eROSITA cluster and cosmology crew from 2019 until the top of 2023.

He is also a member of the Transdisciplinary Analysis Space (TRA) “Matter” of the College of Bonn. The evaluation of the “KiDS” weak lensing survey and in addition the detailed comparability between all three of the surveys is offered right this moment in a paper, additionally posted as a preprint on arXiv and led by Florian Kleinebreil, Ph.D. pupil within the group of Prof. Dr. Tim Schrabback.

A serious a part of this work was performed at AIfA, till each moved to the College of Innsbruck within the fall of 2022. “We discovered that the three lensing surveys yield constant mass constraints for the eROSITA clusters, offering an vital consistency check for the general evaluation,” explains Kleinebreil.

“The finished evaluation demonstrates the excellent cosmological constraining energy supplied by mixed analyses of state-of-the-art galaxy cluster samples and weak lensing surveys. Excitingly, this area will additional advance within the coming years, additionally because of the arrival of next-generation weak lensing packages, together with the one performed by ESA’s new space telescope Euclid,” provides Schrabback.