# High resolution modeling of [CII], [CI], [OIII] and CO line emission from the ISM and CGM of a star forming galaxy at z ~ 6.5

**Authors:** Alice Schimek, Davide Decataldo, Sijing Shen, Claudia Cicone, Bernhard Baumschlager, Eelco van Kampen, Pamela Klaassen, Piero Madau, Luca Di Mascolo, Isabel Montoya Arroyave, Tony Mroczkowski, Jessie Harvir Kaur Warraich  
**arXiv:** [2306.00583](https://arxiv.org/abs/2306.00583)  
**Date:** 2023-06-01  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.00583v1/

## Key points

- Circumgalactic medium (CGM) is a crucial element in galaxy evolution, but its physical properties are largely unexplored.
- Researchers focus on modeling line emissions ([CII], [CI](1-0), [CI](2-1), CO(3-2), and [OIII]) from galaxies using the Ponos simulation at redshift z = 6.5.
- Primary model incorporates radiative transfer post-processing with RamsesRT and Krome to generate realistic far-ultraviolet (FUV) radiation fields.
- [CII] is the least model-dependent gas tracer, while [CI](1-0) and CO(3-2) are highly sensitive to modeling choices.
- Emission contributions from both [CII] (up to 10%) and [OIII] (up to 20%) originate from the CGM, tracing distinct regions within it.
- Implications of findings discussed in relation to current observations with instruments like ALMA and future prospects with AtLAST.

## Summary

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The authors delve into the intricate realm of the circumgalactic medium (CGM), a pivotal element in the evolution of galaxies that remains largely unexplored in terms of its physical properties. Despite numerous cosmological simulations, none have yet achieved convergence in accurately determining the cold and dense gas fraction within the CGM. To address this gap in knowledge, the researchers present a cutting-edge theoretical endeavor focused on modeling line emissions – specifically [CII], [CI](1-0), [CI](2-1), CO(3-2), and [OIII) – from galaxies. Utilizing the high-resolution cosmological zoom-in simulation Ponos, which represents a star-forming galaxy system at redshift z = 6.5 with a stellar mass of $2\times10^9~M_{\odot}$ undergoing a major merger, they employ various modeling approaches based on the photoionization code Cloudy. The team's primary model incorporates radiative transfer post-processing using RamsesRT and Krome to generate realistic far-ultraviolet (FUV) radiation fields. This approach is compared against sub-grid modeling techniques found in existing literature, revealing significant disparities in luminosity and contributions from different gas phases and galaxy components across various models. Notably, [CII] emerges as the least model-dependent gas tracer, while [CI](1-0) and CO(3-2) exhibit high sensitivity to modeling choices. Regardless of the specific model used, all simulations indicate a substantial emission contribution from both [CII] (up to approximately 10%) and [OIII] (up to around 20%) originating from the CGM. Interestingly, distinct regions within the CGM are traced by these emission lines: [CII] is associated with accreting filaments and tidal tails, whereas [OIII] predominantly delineates a puffy halo enveloping the main galactic disk likely influenced by supernova feedback processes. The implications of these findings are discussed within the context of current observations conducted with instruments like ALMA as well as future prospects with AtLAST. By refining our understanding of how different emission lines reflect various regions within galaxies' CGMs, this study contributes valuable insights towards unraveling the complexities of galactic evolution and sheds light on avenues for further exploration in this dynamic field of research.