[IPARCOS astro-seminar] Mr. Clayton Strawn, Wednesday, June 2nd 2021 @

[IPARCOS astro-seminar] 02/06/2021
Mr. Clayton Strawn (UCSC, USA)
PI streams and CI interfaces: How different ionization mechanisms can distinguish phases in the CGM
Abstract: Using ionization modeling software CLOUDY, I present a new definition, based on physical principles, of photoionized (PI) and collisionally ionized (CI) "phases" for individual astrophysical ions. This is unlike how previous authors have usually identified entire clouds (with many ions) as "in PI/CI equilibrium". In the Circumgalactic medium (CGM), gas is highly ionized, and this distinction about how it becomes ionized could have major implications for inferring overall metal masses and interpreting observations. Applying this distinction to OVI in the CGM of a cosmological simulation, I find that PI OVI is identifiable as inflowing cold streams, while CI OVI can be identified as two-phase: the bulk volume and an interface layer between the streams and bulk. The photoionized component dominates observed column densities at large impact parameters (≳0.3Rvir), while the collisionally ionized component dominates closer in. However, this is because the vast majority of CI OVI resides in the relatively thin boundaries of the photoionized streams. I discuss how the simulation results are in realistic agreement with analytic predictions of stream and boundary properties, and their compatibility with observations. All of this together allows us to present a model of the CGM where OVI and other ions would be distributed among the three phases (inflowing and narrowing cool streams, hot and outflowing bulk, thin interface), and would under certain conditions have densities which are approximately powerlaws with galactic radius in each phase. Finally, I will discuss future work which would allow us to more closely refine and modify this model, via theoretical comparisons, and allow us to test this model's applicability, via comparison to observation.