# The nature of the [CII] emission in dusty star-forming galaxies from the SPT-survey

**Authors:** Bitten Gullberg, Carlos De Breuck, Joaquin Vieira, Axel Weiss, James Aguirre, Manuel Aravena, Matthieu Béthermin, C. Matt Bradford, Matt Bothwell, John Carlstrom, Scott Chapman, Chris Fassnacht, Anthony Gonzalez, Thomas Greve, Yashar Hezavah, William L. Holtzapfel, Kate Husband, Jingzhe Ma, Matt Malkan, Dan Marrone  
**arXiv:** [1501.06909](https://arxiv.org/abs/1501.06909)  
**Date:** 2015-01-27  
**Summary page:** https://www.summarizepaper.com/en/paper/1501.06909v1/

## Key points

- Study conducted [CII] observations of 20 strongly lensed dusty star-forming galaxies at redshifts 2.1 to 5.7 using APEX and Herschel telescopes
- Selection based on 1.4 mm flux (S_1.4mm > 20 mJy) from South Pole Telescope survey, with FIR luminosities determined through extensive photometric data analysis
- [CII] line robustly detected in 17 out of the 20 sources, with most being spectrally resolved; eleven sources also showed low-J CO detections from ATCA
- Consistent velocity profiles between [CII] and CO indicated minimal differential lensing effects between these species
- Combined [CII], low-J CO, and FIR data to constrain properties of interstellar medium within galaxies
- Found [CII] to CO(1-0) luminosity ratio in SPT sample of 5200 +- 1800, showing less scatter compared to other samples
- Line ratio best described by a medium with higher excitation temperature for [CII] than for CO, high CO optical depth (tau_CO >> 1), and low to moderate [CII] optical depth (tau_CII ~< 1), attributed to geometric structure of photodissociation regions within galaxies

## Summary

In this study, [CII] observations of 20 strongly lensed dusty star-forming galaxies at redshifts ranging from 2.1 to 5.7 were conducted using the APEX and Herschel telescopes. The selection of these sources was based on their 1.4 mm flux (S_1.4mm > 20 mJy) from the South Pole Telescope survey, with far-infrared (FIR) luminosities determined through extensive photometric data analysis. The results revealed that the [CII] line was robustly detected in 17 out of the 20 sources, with all but one being spectrally resolved. Additionally, eleven of these sources also showed low-J CO detections from ATCA. Comparison with mid- and high-J CO lines from ALMA indicated consistent velocity profiles between [CII] and CO, suggesting minimal differential lensing effects between these species. By combining the [CII], low-J CO, and FIR data, the researchers were able to constrain the properties of the interstellar medium within these galaxies. The study found a [CII] to CO(1-0) luminosity ratio in the SPT sample of 5200 +- 1800, which exhibited significantly less scatter compared to other samples. Further analysis suggested that this line ratio could be best described by a medium consisting of [CII] and CO emitting gas with a higher excitation temperature for [CII] than for CO, high CO optical depth (tau_CO >> 1), and low to moderate [CII] optical depth (tau_CII ~< 1). These conditions were attributed to the geometric structure of photodissociation regions within the galaxies. Overall, this study provides valuable insights into the nature of [CII] emission in dusty star-forming galaxies and sheds light on the properties of their interstellar medium through detailed observational analysis and interpretation.