טכניון מכון טכנולוגי לישראל
הטכניון מכון טכנולוגי לישראל - בית הספר ללימודי מוסמכים  
Ph.D Thesis
Ph.D StudentPeretz Uria
SubjectThe Environment of Active Galactic Nuclei in X-rays
DepartmentDepartment of Physics
Supervisor Professor Ehud Behar


Abstract

Active Galactic Nuclei (AGN) are massive black holes (BHs) at the centers of galaxies, accreting matter which emits profusely at all wavelengths. These massive objects are critical for the understanding of galaxy evolution and the early universe. My PhD centered on finding a physical picture of the environment surrounding the AGN. This environment is highly complex and energetic as seen by their X-ray spectra, showing evidence of several components, most interestingly - an accretion disk; a hot plasma, the corona; and massive, ionized winds. Many open questions remain - What heats the corona, and how is it created? What is its geometry? What drives the massive out ows? This work revolved around defining and measuring quantities of X-ray spectra clarifying the picture.

In the first part of the present thesis we measure outflow properties such as distance from the AGN, electron density, and degree of ionization, relating the outflow both to the central BH and to the surrounding galaxy. The former is important to distinguish between different possible launching mechanisms of these massive winds, such as line driving, magnetic, or others. The latter is how we relate the AGN to the surrounding matter, and measures its importance to the galaxy's evolution, and on what scale if at all.

This work continues by shedding light on the geometric placement of the corona using broadband spectral variability. By defining a quantity relating the more energetic (hard) and the less energetic (soft) part of the X-ray spectrum, we use a statistical analysis of broadband spectra to measure how AGN X-ray spectral behavior changes as their luminosity increases. We find both a connection to X-ray binary systems where there is a much lighter central BH, of the order of a few solar masses, and find a possible evolution track for AGN as their spectral signature changes. This track can be directly related to the location of the corona in the AGN environment.

Finally, the present thesis focuses on an interesting case study. The spectra of NGC4051, an highly variable AGN, shows emission lines usually not clearly discerned in AGN spectra, which allows accurate density and distance diagnostics. This has allowed the first measurements of the broad line region (BLR) in X-rays, a region farther away from the AGN and typically only observed in UV and optical wavelengths. This unique example allowed us to probe further the interaction of the AGN with its outermost surroundings, and determine the extent of the effect these massive objects have around them.

This work aims to further the understanding of the complex structure of the AGN environment, and its intricate interaction with the host galaxy.