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Unveiling the Nature of the Circumgalactic Medium using Cloud-by-cloud, Multiphase, Bayesian Ionization Modeling Methods

Presentation #427.06D in the session Intergalactic Medium, QSO Absorption Line Systems.

Published onJun 29, 2022
Unveiling the Nature of the Circumgalactic Medium using Cloud-by-cloud, Multiphase, Bayesian Ionization Modeling Methods

According to cosmological simulations, galaxies accrete intergalactic gas to fuel star formation, while supernova-driven and AGN outflows pump chemically enriched gas into the CGM and IGM. The cosmic environment influences these large-scale circulation processes between galaxies and the IGM/CGM, necessitating the use of huge and wide-wavelength coverage spectral data sets to statistically characterize them. The CGM and IGM in external galaxies is studied primarily through absorption lines seen in quasar spectra. In this dissertation, I combine an inverse modeling framework (CLOUDY photoionization code) with Nested sampling Bayesian inference to help establish direct connections between the diverse properties derived from characterizing the absorbers and the multiple physical processes at play in the IGM/CGM, and in turn better understand the formation and evolution of galaxies over cosmic time.

A coherent and logical picture of the medium surrounding galaxies is beginning to emerge from the absorption line data, however, there are some significant problems plaguing the interpretations. Often the total column density of a given metal line transition is compared to the total column density of hydrogen to derive a single value for metallicity, ignoring the possibility of multiple phases contributing to an absorption component.

In Sameer et al. 2021, I presented a new method aimed at improving the efficiency of component by component ionization modeling, and show that the properties differ from component to component across the absorption profile.

In Sameer et al. 2022, I investigated the physicochemical properties of the giant HI ring in the Leo I galaxy group probed using 11 quasar sightlines. The origin of the Leo Ring has been a subject of dispute – inflowing material or tidal debris from an interaction. I found that the metallicities of the Leo Ring region to be solar or several times solar, favoring an origin of the HI ring in the aftermath of galaxy-galaxy interaction. I will also present an investigation (Sameer et al. in prep) of the relationship between properties of galaxies and their line-of-sight orientation, using a sample of 47 galaxy-QSO pairs at low-z. The knowledge gained from understanding the physical processes that shape the CGM in low redshift galaxies can be applied to tracing galaxy evolution back to the cosmic dawn.

Finally, I will discuss the learnings from the application of this novel ionization modeling approach to theoretical simulations. These results will inform important decisions about the sub grid physics, critical to making simulations more realistic.

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