Astrophysics of galaxy clusters and groups with eROSITA

Bahar, Yunus Emre (2024): Astrophysics of galaxy clusters and groups with eROSITA. Dissertation, LMU München: Fakultät für Physik

Abstract

This thesis investigates non-gravitational astrophysical phenomena shaping the physical properties of galaxy clusters and groups. The impact of these processes is constrained by measuring the physical properties of galaxy clusters and groups using X-ray observations of eROSITA. The constraints are contextualized by comparing the eROSITA measurements with the predictions of the simple spherical collapse scenario and the predictions of cosmological hydrodynamical simulations. The results presented in this thesis provide a broad view of the population properties of galaxy clusters and groups and serve as a benchmark for unraveling the non-gravitational mechanisms governing cosmic structures. In this thesis, we first focus on the X-ray scaling relations of galaxy clusters and groups. We calibrate seven X-ray scaling relations, accounting for selection effects and the halo mass function, using eROSITA observations of 265 galaxy clusters and groups detected in the eFEDS field. The sample is obtained by applying selection procedures that are reproducible in eROSITA simulations such that the resulting sample has a well-defined selection function. A Bayesian framework is employed to fit the relations, incorporating a custom selection function and a canonical halo mass function to account for selection effects and the mass distribution of halos. Our results show significant deviations from the self-similar model, aligning well with simulations that include prescriptions for non-gravitational mechanisms and recent studies considering selection effects. Our findings suggest that non-gravitational processes significantly influence the physical state of clusters and groups. Our study extends scaling relations to low-mass, low-luminosity parameter space using eFEDS observations. It demonstrates eROSITA's capability to measure intracluster/intragroup medium emission out to r500c with survey-depth exposures and constrain scaling relations across a broad mass-luminosity-redshift range. Second, we focus on the effects of AGN feedback on the entropy and characteristic temperature of galaxy groups detected in SRG/eROSITA's first All-Sky Survey (eRASS1). We analyze eRASS:4 observations of 1178 galaxy groups from the eRASS1 galaxy clusters and groups catalog. We divide the sample into 271 subsamples based on the physical and statistical properties of the groups and jointly analyze their X-ray observations following a Bayesian approach. Through this procedure, we extract average thermodynamic properties, including electron number density, temperature, and entropy, at three characteristic radii (from cores to outskirts) as well as the average integrated temperature within r500c for the 271 group bins. We achieve the tightest constraints with unparalleled statistical precision on the impact of AGN feedback by measuring the average entropy and characteristic temperature of the largest group sample used in X-ray studies. We also quantify the impact of various systematics on our measurements and include their impact to their total error budget. We find that entropy increases with temperature following a power-law relation at higher intra-group medium (IGrM) temperatures, while a slight flattening is observed in cooler (T<1.44 keV) IGrM temperatures. We compare our results with cosmological hydrodynamic simulations (MillenniumTNG, Magneticum, OWL), and find that our entropy measurements at the core lie below the predictions of simulations. At mid-region and outskirts, we find that our measurements align well with the predictions of the Magneticum simulations. Our measurements will facilitate more accurate AGN feedback implementations in numerical simulations. Future eROSITA surveys will extend entropy measurements to even cooler IGrM temperatures, enabling the testing of AGN feedback implementations in this parameter space. Lastly, in this thesis, we explore the thermodynamic property profiles of eROSITA-selected galaxy groups. Previous studies suggest significant differences between the profiles of thermodynamic properties of groups and clusters due to groups having shallower potential wells and, therefore, being more sensitive to non-gravitational processes. In our study, we measure the density, temperature, entropy, and pressure profiles of 1178 galaxy groups using eROSITA observations. The sample used in this study is identical to the one employed in our second study and, therefore, has a well-defined selection function. We obtain tight constraints on the average scaled thermodynamic profiles of X-ray bright groups by normalizing thermodynamic profiles with the self-similar model predictions. Comparing scaled profiles with previous cluster and group measurements, we find that the scaled density profiles of groups are significantly below the scaled density profiles of clusters. Our finding confirms previous studies suggesting groups to be baryon depleted within r500c. We also find that the scaled entropy profiles of groups are considerably higher than clusters at all radii, highlighting AGN's more significant impact on the IGrM compared to the ICM. We compare our measurements with predictions of the non-radiative hydrodynamical simulations, which serve as baselines, and found that the non-gravitational processes decrease groups' scaled density and pressure profiles while increasing the scaled entropy and temperature profiles. Furthermore, we apply our selection function to simulations (Magneticum, MillenniumTNG) that include different AGN feedback models and compare our results with their predictions. We find that Magneticum reproduces our measurements the best at the intermediate radii and outskirts, while our measurements at the core agree better with MillenniumTNG. We further find that our entropy measurements lie below the predictions of simulation at the core and above their prediction at the outskirts, suggesting the excess entropy introduced by the central AGN at the core cannot be efficiently carried to larger radii in the current AGN feedback implementations.

• Dokumententyp: Dissertationen (Dissertation, LMU München)
• Themengebiete: 500 Naturwissenschaften und Mathematik ; 500 Naturwissenschaften und Mathematik > 530 Physik
• Fakultäten: Fakultät für Physik
• Sprache der Hochschulschrift: Englisch
• Datum der mündlichen Prüfung: 15. Oktober 2024
• 1. Bericht­erstatter:in: Nandra, Kirpal