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AR 14286 (Archival Research)

Sat Jul 20 09:12:56 GMT 2024

Principal Investigator: Marios Chatzikos
PI Institution: University of Kentucky
Investigators (xml)

Title: Deciphering the Fossil Record in Quasar Ionization Echoes
Cycle: 23

Abstract
Objects like Hanny's Voorwerp contain information about the light output of currently weak AGN as it stood 10,000 to 100,000 years ago. They consist of clouds at the outskirts of galaxies, and they are particularly bright in [O III] 5007A. Their value lies in the fact that they provide information on the history of AGN luminosity over timescales that are otherwise inaccessible. Many similar objects have been discovered recently, and their numbers are expected to grow with deep observations at higher redshift, such as those JWST will permit. A tool to faithfully interpret the quasar fossil record is needed. We request funding to bolster our theoretical understanding of quasar ionization echoes. The proposed work will unfold in two parts. In the first part, we will develop infrastructure in the spectral synthesis code Cloudy to model the evolution of optically thin clouds exposed to fading radiation fields. In the second part, we will use this infrastructure to produce diagnostics that can put tight constraints on the cloud age, as well as on the initial AGN luminosity. Cloudy is already being used for the purposes of understanding Voorwerpjes, albeit with static models that do not capture the intricacies of evolving systems. Our work will have an immediate impact on the interpretation of HST observations of these objects, and it will pave the way for future JWST programs.