Another important component of space is the hot gas that fills the space between galaxies. Heated to millions of degrees by gravitational collapse and black hole activity, this gas emits X-rays, creating a diffuse X-ray background. The intensity of this radiation depends on the density and temperature of the gas, which in turn are determined by complex physical processes associated with the evolution of galaxies and galaxy clusters.
Scientists from the University of Oxford and Utrecht University have combined observations from the Dark Energy Survey (DES) and the ROSAT satellite to find for the first time a statistically significant correlation between the cosmic shift and the diffuse X-ray background . This discovery means that the distortions in the shape of galaxies caused by the gravitational influence of dark matter are inextricably linked to the distribution of hot gas in intergalactic space.
This relationship, called cross-correlation, opens up new possibilities for astrophysicists to study the influence of baryonic matter on the formation of large-scale structures in the Universe. By analyzing the correlation between the cosmic shift and X-ray emission, it is possible to obtain information about the distribution of gas in dark matter halos — massive regions surrounding galaxies and galaxy clusters. This distribution, in turn, is sensitive to physical processes that determine the behavior of baryonic matter, such as feedback processes associated with the activity of galactic nuclei and supernova explosions.
In particular, the study made it possible to estimate the mass of halos in which feedback processes lead to the ejection of half of the gas. This value, called the “half mass”, is an important parameter characterizing the efficiency of feedback processes and their influence on the formation of galaxies. In addition, it was possible to determine the polytropic index of gas, which characterizes its thermodynamic properties and allows us to judge how much the gas is compressed and heated in the dark matter halo.
The results obtained are in good agreement with data obtained in other studies devoted to the study of the influence of baryonic matter, for example, in the analysis of data on the fraction of gas in X-ray observations of galaxy clusters. However, the new method, based on the cross-correlation of the cosmic shift and the X-ray background, has a number of significant advantages.
First, it directly uses cosmic shear data, which are most sensitive to baryonic matter effects, avoiding errors associated with indirect measurements of gas properties.
Second, the cross-correlation signal is formed by the collective emission of all large-scale structures, rather than individual objects such as galaxy clusters. This makes the analysis less susceptible to errors in modeling individual objects and allows for more reliable results.
Third, the tomographic nature of the cosmic shift data, that is, the ability to separate galaxies by their distance to us, allows us to study the evolution of gas properties over time, tracking how its distribution and temperature have changed throughout the history of the Universe.
Finally, using the same statistical methods as in standard cosmic shift studies makes it easier to incorporate cross-correlation data into cosmological models, allowing for more accurate and self-consistent pictures of the evolution of the Universe.
The discovery of the cross-correlation of the cosmic shift and the X-ray background is only the beginning of the journey. In the future, a more detailed analysis is planned, which will allow us to refine the results obtained and take into account various factors that can affect the correlation, such as the chemical composition of the intergalactic gas, the influence of gravitational lensing, etc. It is also important to include cross-correlation data in a joint analysis with other cosmological observations, for example, with data on relic radiation, which will allow us to obtain a more complete and consistent picture of the evolution of the Universe.
Although much work remains to be done, the prospects for using cross-correlation in cosmological studies are exciting. Incorporating this method into the analysis of data from future sky surveys such as the Vera Rubin Observatory and Euclid, together with data from X-ray missions such as eROSITA, will significantly improve the accuracy of cosmological constraints and make them more robust to astrophysical uncertainties.
This discovery is a striking example of how seemingly different fields of astrophysics can come together to address fundamental questions about the structure and evolution of our world, opening up new horizons of knowledge in the vast expanses of the Universe.
