Investigating high-energy emission in young radio galaxies

Some of the most intriguing questions about the physics and the evolution of radio galaxies are related to the early stages of their life. The so-called Compact Symmetric Objects (CSOs), defined to be those with radio lobe emission on both sides of an active nucleus and an overall size less than about one kpc, are thought to represent the first stage in the evolutionary path of radio galaxies. CSOs are considered a perfect test bench to study the accretion and ejection processes in the early-born radio galaxies and, in view of their compact dimensions, to investigate the interaction between the expanding radio source and the host galaxy. In fact, an alternative scenario ascribes the compactness of CSOs to an extremely dense interstellar medium of the host galaxy, which can slow down or even completely halt the radio source expansion. For this Thesis work, a mini-sample of three CSOs has been selected based on their detection in the X- and gamma-ray band: 1718-649, 1146+596, and 1843+356. The aim of this work was to investigate the origin of the high-energy emission in these objects, infer their physical properties using the broadband spectral energy distribution, and understand the role of the ambient medium in their evolution. Thanks to the high quality of the X-ray data, I was able to: (i) characterize the spectral properties of the unresolved X-ray emission associated with the CSOs; (ii) investigate the hot gaseous component co-spatial with the CSOs; (iii) measure the intrinsic obscuration of the X-ray emission, hence probe the presence of dense gas. In the second part of the study, I considered the broadband emission of two of the targets against theoretical models for the non-thermal emission of lobes and jets. Modeling of the radio-to-gamma-ray emission has provided estimates of the physical parameters of the young sources (e.g. magnetic field, particle contents, etc.) and of the total jet power, allowing to make predictions on the fate of the sources.