Abstract:
Supernova remnants (SNRs) are the expanding structures left behind by supernova explosions. The explosion drives a shock wave outward, sweeping up and heating the surrounding interstellar medium (ISM). These remnants serve as natural laboratories for studying extreme physics processes, including the origin of cosmic rays (CRs). CRs are relativistic, charged particles which are believed to be effectively accelerated at SNRs' shock fronts. The first part of this thesis focuses on the studies of the SNR HESS J1534-571 and the SNR candidate HESS J1614-518, both identified as strong TeV gamma-ray emitters in the H.E.S.S (High Energy Stereoscopic System) Galactic Plane Survey. We investigate the multiwavelength morphology of these sources and the CR acceleration at their sites. Both HESS J1534-571 and HESS J1614-518 exhibit shell-like structures in radio and/or X-ray wavelengths, correlating with their TeV gamma-ray shells. This correlation confirms the SNR nature of HESS J1614-518 for the first time and suggests that radiation across wavelengths originates from the same CR populations. This allows us to construct spectral energy distributions and constrain high-energy gamma-ray production scenarios. For the two objects presented in this thesis, CR electrons cannot be ruled out as the responsible source for the detected high-energy gamma-rays. In addition, other properties of the SNRs, such as the interaction between shock-induced CRs and localised ambient cool gas, are also presented.
Galaxy clusters are the largest gravitationally collapsed objects in the Universe, consisting of thousands of galaxies, hot gas in the intracluster medium (ICM), and dark matter, making them detectable across a wide range of wavelengths. They are valuable probes to constrain cosmological parameters and to study large-scale physics. However, samples selected by different methods based on different wavebands may represent distinct populations of clusters. Therefore, it is crucial to understand the characteristics of cluster samples and the impact of selection methods for further cosmological and astrophysical applications. The second part of this thesis presents the analyses of the optically selected cluster sample CAMIRA from the Subaru-HSC observations overlapping the eFEDS survey of the SRG/eROSITA X-ray telescope. Initially focusing on ~40 high-richness (N > 40) objects, we expanded the study to ~1000 clusters with lower richness cut (N > 15), examining morphology, scaling relations, and selection effects. We conclude that the optically-based method can effectively select a complete cluster population with diverse ICM characteristics. While optical properties remain relatively uniform across the sample, X-ray properties vary, influencing cluster detectability in X-ray surveys.
Supernova remnants