# JWST Spectroscopic Insights Into the Diversity of Galaxies in the First 500 Myr: Short-Lived Snapshots Along a Common Evolutionary Pathway

## TL;DR

This study uses JWST/NIRSpec data to analyze the spectral diversity of early galaxies within the first 500 million years, revealing that bursty star formation drives observed variations and that AGN are unlikely contributors.

## Contribution

It provides new insights into the role of bursty star formation and spectral diversity in early galaxy evolution, supported by spectroscopic analysis of 41 high-redshift sources.

## Key findings

- Strong CIV emitters are associated with concentrated starbursts.
- Diversity is driven by short-timescale bursty star formation (<3 Myr).
- AGN are unlikely to significantly influence the observed spectral properties.

## Abstract

We investigate the nature and spectroscopic diversity of early galaxies from a sample of 41 sources at z>10 with JWST/NIRSpec prism observations. We compare the properties of strong UV line emitters, traced by intense CIV emission, with those of more "typical" sources with weak or undetected CIV. The more typical (or "CIV-weak") sources reveal significant scatter in their CIII] line strengths, UV continuum slopes, and physical sizes, spanning CIII] equivalent widths of ~1-51 \r{A}, UV slopes of $\beta$~-1.6 to -2.6, and half-light radii of ~50-1000 pc. In contrast, CIV-strong sources occupy the tail of these distributions, with CIII] EWs of 16-51 \r{A}, UV slopes $\beta$<-2.5, compact morphologies ($r_{50}$<100 pc), and elevated star formation surface densities ($\Sigma_{SFR}$>100 $M_{\odot}yr^{-1}kpc^{-2}$). These properties suggest concentrated starbursts that temporarily outshine the host galaxy. Comparing average properties from composite spectra, we find the diversity of the sample is primarily driven by bursty star formation on very short timescales (<3 Myr), with strong CIV emitters observed at the apex of the bursts and sources devoid of emission lines during relative inactivity. An apparent association between strong CIV and enhanced nitrogen abundance suggests both may be modulated by the same duty cycle, reflecting a generic mode of star formation. We show that AGN are unlikely to contribute significantly to this duty cycle based on UV line diagnostics and photoionisation models. Our results support a picture whereby brief bursts and lulls can explain the spectral diversity and early growth of bright galaxies in the first 500 Myr.