# The European Low Frequency Survey

**Authors:** Aniello Mennella, Kam Arnold, Susanna Azzoni, Carlo Baccigalupi, Anthony Banday, R. Belen Barreiro, Darcy Barron, Marco Bersanelli, Sean Casey, Loris Colombo, Elena de la Hoz, Cristian Franceschet, Michael E. Jones, Ricardo T. Genova-Santos, Roger J. Hoyland, Adrian T. Lee, Enrique Martinez-Gonzalez, Filippo Montonati, Jose-Alberto Rubino-Martin, Angela Taylor  
**arXiv:** [2310.16509](https://arxiv.org/abs/2310.16509)  
**Date:** 2023-10-25  
**Summary page:** https://www.summarizepaper.com/en/paper/2310.16509v1/

## Key points

- The European Low Frequency Survey (ELFS) aims to measure primordial B-mode polarization with foregrounds-free measurements.
- Galactic and extra-Galactic emissions will be measured in the 5-120 GHz frequency window.
- The main challenge is the presence of other objects emitting polarized microwaves that mask the faint Cosmic Microwave Background (CMB) signal.
- The first stage of ELFS will be carried out in collaboration with the Simons Array (SA) using a coherent receiver installed at one of the SA telescopes in Atacama, Chile.
- The receiver will have a fully digital back-end providing a frequency resolution of 1 MHz across the observing band.
- High-fidelity subtraction of galactic foreground emission is crucial for detecting primordial gravitational waves generated by inflation after the Big Bang.
- Foreground emissions from Galactic dust and synchrotron radiation pose significant challenges to detecting primordial gravitational waves.
- Synchrotron radiation is less well characterized and potentially more complex than dust, but recent experiments have increased our knowledge about it.
- Low-frequency instruments like ELFS will play a crucial role in constraining and removing synchrotron emission to extract the CMB signal.
- ELFS aims to contribute to our understanding of the early Universe by observing radio sky signals through advanced technology and collaborative efforts.

## Summary

The European Low Frequency Survey (ELFS) is a project aimed at enabling foregrounds-free measurements of primordial B-mode polarization to a level of 10^-3. This is achieved by measuring the Galactic and extra-Galactic emissions in the 5-120 GHz frequency window. The main challenge in measuring B-mode polarization lies not only in its faintness but also in the presence of other objects in the Universe that emit polarized microwaves, which mask the faint Cosmic Microwave Background (CMB) signal. To address this challenge, the first stage of the ELFS project will be carried out in collaboration with the Simons Array (SA) collaboration. A 5.5-11 GHz coherent receiver will be installed at the focus of one of the three 3.5 m SA telescopes in Atacama, Chile, known as "ELFS on SA". This receiver will be equipped with a fully digital back-end based on the latest Xilinx RF System-on-Chip devices, providing a frequency resolution of 1 MHz across the entire observing band. The high-fidelity subtraction of galactic foreground emission is crucial for detecting primordial gravitational waves generated by inflation shortly after the Big Bang. The target sensitivity of r ~ 10^-3 in next-generation CMB experiments like Simons Observatory implies that foregrounds are at least an order of magnitude higher in brightness. Foreground emissions from Galactic dust and synchrotron radiation pose significant challenges to detecting primordial gravitational waves. The complexity and characteristics of these emissions are not yet fully understood. Dust has been extensively studied due to its role in previous false detections, such as those made by BICEP2. However, synchrotron radiation is less well characterized and potentially more complex than dust. Recent ground-based experiments operating in the 2-20 GHz range have increased our knowledge of synchrotron radiation. Data from instruments like S-PASS, C-BASS, and QUIJOTE-MFI have revealed that synchrotron emission is more complex than previously assumed. Low-frequency instruments will play a crucial role in constraining and removing synchrotron emission to extract the CMB signal. The ELFS project aims to contribute to our understanding of the early Universe by observing radio sky signals through advanced technology combined with collaborative efforts to achieve foregrounds free measurements for primordial B mode polarization which can shed light on how our universe began.