# CONCERTO: Extracting the power spectrum of the [C II ] emission line

**Authors:** M. Van Cuyck, N. Ponthieu, G. Lagache, A. Beelen, M. Béthermin, A. Gkogkou, M. Aravena, A. Benoit, J. Bounmy, M. Calvo, A. Catalano, F. X. Désert, F. -X. Dupé, A. Fasano, A. Ferrara, J. Goupy, C. Hoarau, W. Hu, J. -C Lambert, J. F. Macías-Pérez  
**arXiv:** [2306.01568](https://arxiv.org/abs/2306.01568)  
**Date:** 2023-06-02  
**Summary page:** https://www.summarizepaper.com/en/paper/2306.01568v1/

## Key points

- CONCERTO aims to perform a [CII] line intensity mapping survey targeting redshifts greater than 5.2
- The power spectrum of [CII] can be used to study the role of dusty star-forming galaxies in the star formation history during Reionization and post-Reionization
- Contamination by bright foregrounds is a main challenge in this measurement
- The authors evaluated their ability to retrieve the [CII] signal using mock observations from the Simulated Infrared Dusty Extragalactic Sky
- Two methods for dealing with dust continuum emission from galaxies were compared: standard principal component analysis (PCA) and adaptive robust iterative polynomial least-squares (arPLS) method
- Line interlopers were masked using external catalogues as they did not have observations of CO or classical CO proxies, and the COSMOS stellar mass catalogue was used for this purpose
- The arPLS method achieved a reduction of the continuum background to a sub-dominant level of [CII] at z=7 by a factor greater than 70, while PCA only achieved a factor of 0.7
- Masking lowered the power amplitude of line contamination down to $2 \times 10^2 Jy^2/sr$, which was dominated by faint undetected sources.
- For their [CII] model, they detected a power ratio [CII]/(residual interlopers) = $62 \pm 32$ at z=5.2 for a 22% area survey loss but only found [C II ] / (residual interlopers)$=2.0 \pm 1.4$ at z=7.
- The authors presented an end-to-end simulation of extragalactic foreground removal that they ran to detect [CII] at high redshift via its power spectrum.
- Dust continuum emission was not a limiting foreground for [CII] LIM, but residual CO and [CI] limited their ability to measure the [CII] power spectrum at z>7.
- The paper is organized into sections on motivation and goals, observational strategy and data analysis methods, results on masking low-redshift galaxies, removing dust continuum emission, and measuring the [CII] power spectrum using different techniques. The authors also discuss the implications of their findings for future studies of high-redshift star-forming galaxies and suggest further research.

## Summary

CONCERTO is a groundbreaking experiment that aims to perform a [CII] line intensity mapping survey targeting redshifts greater than 5.2. By measuring the power spectrum of [CII], we can study the role of dusty star-forming galaxies in the star formation history during Reionization and post-Reionization. However, one of the main challenges in this measurement is contamination by bright foregrounds. To overcome this obstacle, the authors evaluated their ability to retrieve the [CII] signal using mock observations from the Simulated Infrared Dusty Extragalactic Sky. The authors compared two methods for dealing with dust continuum emission from galaxies: standard principal component analysis (PCA) and adaptive robust iterative polynomial least-squares (arPLS) method. For line interlopers, they relied on masking low-redshift galaxies using external catalogues as they did not have observations of CO or classical CO proxies. The COSMOS stellar mass catalogue was used for this purpose. To measure the power spectrum of masked data, they adapted the P of K EstimatoR and discussed its use on LIM data. The arPLS method achieved a reduction of the continuum background to a sub-dominant level of [CII] at z=7 by a factor greater than 70, while PCA only achieved a factor of 0.7. Masking lowered the power amplitude of line contamination down to $2 \times 10^2 Jy^2/sr$, which was dominated by faint undetected sources. For their [CII] model, they detected a power ratio [CII]/(residual interlopers) = $62 \pm 32$ at z=5.2 for a 22% area survey loss but only found [C II ] / (residual interlopers)$=2.0 \pm 1.4$ at z=7. The authors showed that the power amplitude of line residuals varied by 12-15% for z=5.2-7, thanks to the large area covered by SIDES-Uchuu. The authors presented an end-to-end simulation of extragalactic foreground removal that they ran to detect [CII] at high redshift via its power spectrum. They demonstrated that dust continuum emission was not a limiting foreground for [CII] LIM, but residual CO and [CI] limited their ability to measure the [CII] power spectrum at z>7. The paper is organized as follows: after introducing the motivation and goals of CONCERTO, the authors describe their observational strategy and data analysis methods in detail. They then present their results on masking low-redshift galaxies, removing dust continuum emission, and measuring the [CII] power spectrum using different techniques. Finally, they discuss the implications of their findings for future studies of high-redshift star-forming galaxies and conclude with suggestions for further research.