A high-resolution study of powerful winds in highly accreting supermassive black holes

An active galactic nucleus (AGN) is powered by the accretion of matter infalling onto a supermassive black hole (SMBH), found at the core of most galaxies. The accretion process releases an enormous amount of radiation, while concurrently propelling matter away through winds, especially for those accreting approach or exceed the Eddington limit. Black holes at Eddington accretion rates are growing fast but are also expected to launch powerful winds of hot plasmas due to the extreme radiation pressure from the underlying accretion disk. These outflows, when intersecting our line of sight to the radiation source, leave imprints in X-ray spectra of the accretion disk in the form of Doppler-shifted lines. AGN winds play a critical role in regulating SMBH growth and the host galaxy’s evolution by carrying away a significant portion of infalling matter. Notably, certain AGN outflows, known as ultra-fast outflows (UFOs), can achieve speeds exceeding 3% and even reach 30% of the speed of light. Due to their extreme velocities, UFOs are regarded as a promising candidate to affect the galaxy evolution by depositing significant kinetic energy into the surrounding gas, thereby heating the interstellar medium and quenching the star formation rate of the host galaxy. However, the uncertainties in the geometries, launching mechanisms and outflow rates of such outflows imply a substantial uncertainty in determining their effects on SMBH evolution and the impacts on host galaxies. By using both the currently most advanced photoionization modelling method and the data from the by far best instrument for soft X-ray high-resolution spectroscopy, XMM-Newton Reflection Grating Spectrometer (RGS), I studied the nature of UFOs in soft X-ray bands of a super-Eddington narrow-line Seyfert 1 (NLS1) galaxy and a high-Eddington NLS1 AGN and extend the analysis to a large sample of high-Eddington AGN. UFOs in the soft X-ray bands are largely overlooked before my works and commonly exhibit a cool temperature. My results reveal that UFOs in these systems are driven by the radiation pressure and are sufficiently energetic to affect the evolution of their host galaxies, while the radiative acceleration may decrease as the accretion rate increases, probably due to the change in the geometry of accretion flows. Additionally, I also achieved the first discovery of evidence for the connection between the accretion inflows and UFOs in the soft X-ray band of an NLS1 galaxy.