# Lyman and Balmer breaks reveal mature z=8 galaxies with the code Pegase.3

## TL;DR

This study uses spectral energy distribution modeling with Pegase.3 to reveal that certain z=8 galaxies are mature, massive, and have Balmer breaks indicating ages of around 450-500 million years, challenging earlier notions of galaxy formation.

## Contribution

It demonstrates the use of Pegase.3 to identify mature, massive galaxies at z=8 through Balmer break analysis, providing new insights into early galaxy evolution.

## Key findings

- Galaxies have ages of 450-500 Myrs based on Balmer break analysis.
- Massive galaxies with stellar masses around 7×10^10 Msun were identified.
- Results suggest rapid formation of elliptical galaxies, impacting reionization models.

## Abstract

The z=8 galaxy sample (EGSY-2008532660, EGS-zs8-1, EGS-zs8-2), observed with HST and Spitzer/IRAC, was selected for its atypical [3.6]-[4.5]mum IR excess. The best-fitting of observations is processed with multiple libraries of continuous UV-to-farIR spectral energy distributions (SEDs) with the help of the code Pegase.3 with dust (Fioc and Rocca-Volmerange, 2018, submitted to AA). The main results are: i) the IR excess is due to the Balmer break of red giant stars with galaxy ages of 450-500 Myrs ii) masses are high: 7 10^10 Msun for stellar mass, 10^11 Msun for galaxy mass, 3 10^8 Msun for dust mass iii) they are probing mature (no starbursting) galaxies only with the simulations of spheroidal (and no spiral) geometries and the star formation history (SFH ) of massive ellipticals. Less constrained by observations not covering the Balmer zone, the galaxy GN-z11 is consistent. These results constrain the rapid and efficient formation of massive elliptical galaxies, significantly distinct of early-type disk-spiral galaxies, and the reionization of the Universe