# First Light And Reionisation Epoch Simulations (FLARES) III: The properties of massive dusty galaxies at cosmic dawn

**Authors:** Aswin P. Vijayan, Stephen M. Wilkins, Christopher C. Lovell, Peter A. Thomas, Peter Camps, Maarten Baes, James Trayford, Jussi Kuusisto, William J. Roper  
**arXiv:** [2108.00830](https://arxiv.org/abs/2108.00830)  
**Date:** 2021-08-02  
**Summary page:** https://www.summarizepaper.com/en/paper/2108.00830v1/

## Key points

- The study utilizes the Flares simulations to investigate high-redshift galaxies at redshifts ranging from 5 to 10.
- The researchers use the radiative transfer code SKIRT to generate full spectral energy distributions (SEDs) of the simulated galaxy sample.
- The main focus of the analysis is on exploring luminosity functions, IRX-β relations, and luminosity-weighted dust temperatures during the Epoch of Reionisation (EoR).
- Results generally align with current observations but under-predict the number densities of bright infrared (IR) galaxies, which are biased towards regions with higher overdensities.
- The IRX-β relation derived from Flares closely follows the local starburst relation for redshifts between 5 and 8.
- IRX increases with stellar mass and plateaus at high masses (~10^10 solar masses), showing no evolution in median normalization with redshift.
- Strongest correlation found between peak dust temperature (T_peak) and specific star formation rate (sSFR).
- Luminosity-weighted dust temperatures increase as redshift increases, with a steeper slope compared to previous works at lower redshifts.
- Flares provides a more extensive statistical sample of high-redshift galaxies compared to other simulations, allowing for a unique perspective on studying the high-redshift Universe.
- Zoom simulations using Flares and the Eagle model aim to investigate how well the physics model can replicate the high-redshift Universe in comparison to infrared observations.
- The paper is organized into sections discussing simulations used, results obtained from Flares, and conclusions drawn from this study.

## Summary

In this study, the authors utilize the First Light And Reionisation Epoch Simulations (Flares) to investigate the properties of massive high-redshift galaxies at redshifts ranging from 5 to 10. To obtain a comprehensive understanding of these galaxies, the researchers post-process the simulated galaxy sample using the radiative transfer code SKIRT, allowing them to generate full spectral energy distributions (SEDs). The main focus of their analysis is on exploring luminosity functions, IRX-β relations, and luminosity-weighted dust temperatures during the Epoch of Reionisation (EoR). The results obtained from Flares generally align with current observations; however, there is an under-prediction in the number densities of bright infrared (IR) galaxies. These galaxies are found to be highly biased towards regions with higher overdensities. The IRX-β relation derived from Flares for redshifts between 5 and 8 closely follows the local starburst relation. Additionally, it is observed that IRX increases with stellar mass and plateaus at high masses (~10^10 solar masses), while showing no evolution in median normalization with redshift. The study also investigates the relationship between peak dust temperature (T_peak) and various galaxy properties such as stellar mass, IR luminosity, and specific star formation rate (sSFR). The strongest correlation is found between T_peak and sSFR. Furthermore, it is noted that luminosity-weighted dust temperatures increase as redshift increases. The slope of the T_peak-redshift relation in Flares exhibits a steeper trend compared to previous observational and theoretical works conducted at lower redshifts. One significant advantage of using Flares is its ability to provide a more extensive statistical sample of high-redshift galaxies compared to other simulations. This allows for a unique perspective on studying the high-redshift Universe. To overcome limitations in obtaining a representative statistical sample of massive galaxies during the EoR, the authors conducted a suite of zoom simulations using Flares. These simulations utilize the well-established Eagle model, which has been shown to accurately reproduce various observables at both low and high redshifts. By post-processing these simulations with SKIRT, the researchers aim to investigate how well the Eagle physics model can replicate the high-redshift Universe, particularly in comparison to infrared observations such as luminosity functions, IRX-β relations, and luminosity-weighted dust temperatures. The paper is organized as follows: Section 2 introduces the suite of simulations used in this study, along with details about the galaxy sample and SED generation method. Section 3 presents results obtained from Flares including analyses of UV and IR luminosities (Section 3.1), IRX–β relation (Section 3.2), variations and evolution of dust temperatures (Section 3.3). Finally Section 4 summarizes findings and conclusions drawn from this study. In addition to observational efforts it is crucial to explore theoretical models of galaxy formation and evolution to understand nature of dusty high–redshift systems fully . Several studies have employed semi–analytical or analytical techniques as well as hydrodynamical models successfully investigating observed properties of galaxies at high redshifts . Hydrodynamical simulations offer more detailed representation dark matter , gas , stars , black holes' evolution compared semi–analytical models . However current state–of–the–art cosmological simulation periodic boxes often lack sufficient number massive galaxies during EoR due computational limitations . This limitation hinders their statistical power studying bright galaxies discovered by current future telescopes .