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Time Dependent Photoionization of Warm Absorbers Found in Active Galactic Nuclei.

Published onJun 01, 2020
Time Dependent Photoionization of Warm Absorbers Found in Active Galactic Nuclei.

Hot and ionized plasma coming out from the center of active galactic nuclei is termed as warm absorbers. Absorption lines and edges in UV and X-ray of AGN warm absorbers have been studied over long period of time. However, fundamental properties of warm absorbers like: 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. 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. Which potentially can reach to ISM and can have impact on the chemical evolution and star formation process in the host galaxy. This could even reach to intergalactic medium and enrich it with heavier elements called the feedback mechanism. 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 ongoing research is about inclusion of time dependence in the photoionization code XSTAR, which has already been developed. 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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