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Time Dependent Photoionization in AGN Warm Absorbers

Presentation #312.06 in the session “Laboratory Astrophysics Division (LAD): Astrochemistry II”.

Published onJun 18, 2021
Time Dependent Photoionization in AGN Warm Absorbers

Different properties of astrophysical object now a days can be obtained by rigorous study of the complex emission or absorption spectra. Composition, ionization and excitation state, motion of the constituent particle are the important properties which can be found from those spectra. AGN Warm Absorber absorption line and edges in UV and X-ray is one of them and has been extensively studied over last few decades. Blue shifted absorption lines in the spectra reveal the presence of massive outflows of ionized gas from their nuclei at speed of ∼ 1000 Km/s. Dynamical model for outflow makes the use of thermal wind, radiation pressure and/or hydrodynamic flows, which has reached a level of sophistication that permits comparison with observation. However, fundamental properties of warm absorbers: What is the mechanism which drives the outflow? What is the gas density in the flow and the geometrical distribution of the outflow? Where does the outflow originate and what is its fate? Do ionized outflows play an important role on the host galaxy chemical history and evolution? are not determined precisely and are of great interest. Intrinsic UV and X-ray absorbers show large global covering factors of the central continuum source. Researchers have found that mass loss rate via WA is comparable to the mass accretion rate by putative central black hole. Outflows in Active Galactic Nuclei (AGN) is supposed to play an important role in the evolution of their host galaxy and on the enrichment of the intergalactic medium. In the X-ray range, the outflows appear as a warm absorber (WA) gas displaying high bulk velocities. Which potentially can reach to ISM and can have impact on the chemical evolution and star formation process in the host galaxy. Also, the resulting mass outflow rate can be a substantial fraction of the accretion rate required to power the AGN. Thus, WA can be dynamically important and the knowledge of their state, location, geometry and dynamics would help in understanding the central engines of AGN. Progress towards understanding warm absorbers is limited by the assumption used so far in photoionization modeling: that the gas is in ionization and excitation equilibrium. This is almost certainly not correct in detail; the dynamical timescales in the flow are comparable to or less than the timescales characterizing the ionization and excitation, and the inverse processes in the gas responsible for the lines we observe. Which means the gas departs from equilibrium and so temporal dependency for ionization, heating & cooling and radiative transfer equation has to be included in the modeling of the absorber. The topic of the proposed research is the inclusion of time dependence in the photoionization code which has already been developed, Xstar. The goal is to do this in a way which is as general and computationally efficient as possible. Then we will use this code for self-consistent calculations of warm absorber dynamics.


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