# Observations of neutral carbon in 29 high-z lensed dusty star forming galaxies and the comparison of gas mass tracers

**Authors:** G. Gururajan, M. Béthermin, N. Sulzenauer, P. Theulé, J. S. Spilker, M. Aravena, S. C. Chapman, A. Gonzalez, T. R. Greve, D. Narayanan, C. Reuter, J. D. Vieira, A. Weiss  
**arXiv:** [2306.03153](https://arxiv.org/abs/2306.03153)  
**Date:** 2023-06-05  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.03153v1/

## Key points

- High-redshift dusty star-forming galaxies (high-z DSFGs) have massive gas reservoirs that drive intense star-formation rates
- Various gas mass tracers such as [CI], CO, [CII] emission lines and dust content are used to estimate molecular gas content of high-z DSFGs
- Uncertainties on factors such as aCO, XCI, aCII and GDR can limit the accuracy of these tracers
- Observations were carried out for 29 SPT-SMGs using ALMA-ACA to observe two [CI] line transitions and new APEX observations of [CII] line were presented for nine of these galaxies
- Results show a nearly linear relation between infrared luminosity and [CI] luminosity when fitting starbursts and main-sequence galaxies separately; median excitation temperature derived from [CI] was found to be 34.5+/-2.1 K
- Properties of interstellar medium (ISM), such as density and radiation field intensity, were probed using [CI] to mid- or high-J CO lines and [CI] to infrared luminosity ratio; similar values were found compared to SMG populations in literature
- Gas masses estimated from various tracers did not exhibit any significant trend with infrared luminosity or dust temperature
- Cross-calibrations between these tracers confirmed that [CI] is a suitable tracer for estimating molecular gas content at high redshift; overall agreement was observed between all classical gas tracers used at high redshift
- Absolute calibration remains uncertain leading to uncertainty in gas depletion timescale measurements
- This study provides important insights into the nature and evolution of high-z DSFGs and highlights the need for further research in this area

## Summary

The study of high-redshift dusty star-forming galaxies (high-z DSFGs) is an area of active research, as their massive gas reservoirs are crucial in driving the intense star-formation rates observed in these galaxies. To estimate the molecular gas content of high-z DSFGs, various gas mass tracers such as [CI], CO, [CII] emission lines and dust content are used. However, uncertainties on factors such as aCO, XCI, aCII and GDR can limit the accuracy of these tracers. The primary goal of this study is to cross-calibrate these uncertain factors and check the consistency between different gas mass tracers. Observations were carried out for 29 SPT-SMGs using ALMA-ACA to observe two [CI] line transitions. Additionally, new APEX observations of [CII] line were presented for nine of these galaxies. The results show a nearly linear relation between infrared luminosity and [CI] luminosity when fitting starbursts and main-sequence galaxies separately. The median excitation temperature derived from [CI] was found to be 34.5+/-2.1 K.

The properties of interstellar medium (ISM), such as density and radiation field intensity, were probed using [CI] to mid- or high-J CO lines and [CI] to infrared luminosity ratio. Similar values were found compared to SMG populations in literature. Gas masses estimated from various tracers including [CI], CO, dust, and [CII], did not exhibit any significant trend with infrared luminosity or dust temperature. Cross-calibrations between these tracers were provided which confirmed that [CI] is a suitable tracer for estimating molecular gas content at high redshift. Overall agreement was observed between all classical gas tracers used at high redshift; however, absolute calibration remains uncertain leading to uncertainty in gas depletion timescale measurements. This study provides important insights into the nature and evolution of high-z DSFGs and highlights the need for further research in this area.