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Exploring the physics and the energetics of low redshift (0.6 < z < 1.5) FeLoBAL outflows

Presentation #529.01 in the session “Quasars”.

Published onJan 11, 2021
Exploring the physics and the energetics of low redshift (0.6 < z < 1.5) FeLoBAL outflows

Broad absorption line quasars (BALQs) exhibit clear evidence for powerful outflows from central supermassive black holes in their rest-UV spectra. These BAL outflows are thought to be one of the main drivers of quasar feedback that influences the star formation rate and the evolution of the host galaxies. FeLoBALQs are a subtype of BALQs that show higher column density outflows with absorption lines from low-ionization ions (e.g., MgII, AlIII) and FeII. They may represent a short-lived step in quasar evolution where the quasar blows out its cocoon of gas and dust (“blowout” phase; e.g., Sanders et al. 1988). FeLoBALQs are thus excellent targets for investigating quasar outflows and feedback on galaxies. We analyzed spectra of 53 FeLoBALQs, measuring the outflow gas properties and estimating kinetic luminosity for all identified BAL outflows using the forward-modeling spectral fitting software SimBAL. We found a large range of physical properties (ionization parameter, density and column density). Notably, the absorbers in the outflows are found from parsecs to kiloparsecs from the central quasar, spanning four orders of magnitude. From the best-fitting SimBAL models, we extracted the opacity profiles of the major transitions found in FeLoBALs to study the substructures of the BAL clouds. The ground state MgII λ2796Å showed the largest width followed by ground state FeII λ2383Å and an excited state FeII λ2757Å. This trend suggests that the BAL outflows are made up of denser cores within larger diffuse gas clouds because both FeII transitions require higher column density than the MgII transition and the excited FeII transitions only appear in high-density gas. Some BAL outflows showed complex opacity profiles where the FeII cores were located at the highest and/or lowest velocity. We will discuss the implications of our result for the origin, structure, stability, and acceleration mechanisms of the FeLoBAL outflows.

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