# [CII] Emission in a Self-Regulated Interstellar Medium

**Authors:** Alon Gurman, Chia-Yu Hu, Amiel Sternberg, Ewine F. van Dishoeck  
**arXiv:** [2308.07338](https://arxiv.org/abs/2308.07338)  
**Date:** 2023-08-11  
**Summary page:** https://www.summarizepaper.com/en/paper/2308.07338v1/

## Key points

- [CII] 157.74 μm line is a prominent emission line in the far-infrared (FIR) region produced in the interstellar medium (ISM) of galaxies
- Sub-pc resolution hydrodynamical simulations used to analyze an ISM patch with gas surface density Σg=10 M⊙ pc−2
- Simulations incorporate various physical processes such as time-dependent chemistry, FUV dust and gas shielding, star formation, photoionization, supernova feedback, and full line-radiative transfer
- Intensity of [CII] 157.74 μm line correlates with star formation rate (SFR) and scales linearly with metallicity
- Reliable tracer for SFR even in metal-poor environments where molecular lines may be difficult to detect
- [CII]-to-H2 conversion factor derived that can be described by a power law relationship with metallicity
- Findings consistent with observations except for lowest metallicity run
- Importance of resolving clumpy structure of dense ISM as it dominates [CII] 157.74 μm emission
- Comparison between full radiative transfer computation and optically-thin limit shows [CII] emission approaches limit at super-solar metallicity for assumed gas surface density
- Acknowledges fruitful discussions with Chris McKee and Reinhard Genzel and support from various funding sources including grants from German Science Foundation, Center for Computational Astrophysics (CCA), Flatiron Institute, and Mathematics and Physical Sciences (MPS) division of Simons Foundation USA

## Summary

In this study, the authors investigate the properties of the [CII] 157.74 μm fine structure transition, which is a prominent emission line in the far-infrared (FIR) region and is produced in the interstellar medium (ISM) of galaxies. They use sub-pc resolution hydrodynamical simulations to analyze an ISM patch with a gas surface density of Σg=10 M⊙ pc−2. The simulations incorporate various physical processes such as time-dependent chemistry, far-ultraviolet (FUV) dust and gas shielding, star formation, photoionization, supernova feedback, and full line-radiative transfer. The results show that the intensity of the [CII] 157.74 μm line correlates with the star formation rate (SFR) and scales linearly with metallicity. This makes it a reliable tracer for SFR even in metal-poor environments where molecular lines may be difficult to detect. The authors also derive a [CII]-to-H2 conversion factor that can be described by a power law relationship with metallicity. Comparing their findings with galaxy surveys, they find that their results are consistent with observations except for the lowest metallicity run. The authors emphasize the importance of resolving the clumpy structure of the dense ISM as it dominates the [CII] 157.74 μm emission. Additionally, they compare their full radiative transfer computation with an optically-thin limit and find that [CII] emission only approaches this limit at super-solar metallicity for their assumed gas surface density. The study acknowledges fruitful discussions with Chris McKee and Reinhard Genzel and acknowledges support from various funding sources including grants from German Science Foundation, Center for Computational Astrophysics (CCA), Flatiron Institute and Mathematics and Physical Sciences (MPS) division of Simons Foundation USA. Overall, this study provides valuable insights into the properties of the [CII] 157.74 μm line and its potential as a tracer for star formation in different environments; highlighting both its reliability even in metal poor environments as well as emphasizing how important it is to consider its clumpy structure when interpreting its emission data from galaxy surveys or other sources..