|M.Sc Student||Holczer Tomer|
|Subject||Studies of X-ray Absorption Spectra Due to Active Galactic|
|Department||Department of Physics||Supervisor||Professor Ehud Behar|
|Full Thesis text|
Outflows from active galactic nuclei (AGNs) can provide an important feedback on the processes controlling the black hole and galaxy evolution. However, their physical properties - such as mass outflow rate and location - are still controversial .
The X-ray emission of many AGNs is absorbed between 15 and 17 Å by means of unresolved (inner-shell) transition arrays (UTAs) of Fe M-shell ions. The outflow velocities implied by the Doppler shifts of the individual UTAs in the spectrum have never before been measured. Thus, the Fe M-shell absorber has been commonly assumed to be part of the ionized AGN outflow, whose velocities are readily obtained from more easily measured spectral lines. The best spectrum of Fe M-shell absorption is available from the integrated 900 ks Chandra HETG observations of NGC 3783, in which some Fe M-shell ions are clearly resolved. We measure the velocities of the individual Fe M-shell ions in NGC 3783 for the first time. Surprisingly, we find that the Fe M-shell absorber, most noticeably Fe+8, Fe+9, and Fe+10, is not outflowing at the same velocity as the previously known wind. In fact, it appears to be stationary and therefore not part of the outflow at all. However, newly calculated atomic data show that the Fe M-shell absorber is actually outflowing at the same velocity as Fe L-shell, O K-shell and other resolved ions.
We analyze the Chandra X-ray spectrum obtained with the HETG grating spectrometer of IRAS 13349+2438, which has one of the richest absorption spectra of a quasar outflow. Absorption from essentially all charge states of Fe is detected. This allows for a detailed reconstruction of the absorption measure distribution (AMD), which we define as the distribution of column density as a function of ionization parameter. We find a double peaked AMD for IRAS 13349+2438 with a total (ionized) column density of NH = (1.2±0.3) × 1022 cm-2 assuming solar iron abundance. For comparison, we perform a similar analysis for the well studied
HETG spectrum of NGC 3783 for which we find NH = (4.1±0.7) × 1022 cm-2. Both sources feature a minimum in column density around ionization parameter values of 0.75 < logξ < 1.75 (c.g.s. units), which corresponds to temperatures of 4.5 < logT < 5 (K). We interpret these minima as observational evidence for thermal instability in this temperature.