• burstiness
• First billion years
• First Gyr
• Galaxies
• High-redshift
• JWST
• Luminosity function
• NIRSpec
• SED
• SFH
• Star formation history

In this thesis I explore the star formation histories of galaxies at redshift z > 6 through the technique of the spectral energy distribution (SED) fitting applied to spectroscopic observations by the JWST NIRSpec spectrograph.
I perform a statistical analysis on the entire sample of the JADES 3rd release. Through the SED fitting I investigate the physical properties of these primordial galaxies, such as mass, star formation rate, and dust extinction to look into correlations between these quantities and for evidence of bursty star formation.
The investigation of the data of these galaxies includes the analysis of mock observations, to find limitations and reliability in the context of high-redshift galaxies of Bagpipes: the package used to perform SED fitting. This thesis also includes modifications to the Bagpipes package to address the difficulties in fitting strong emission lines in some analyzed galaxies.
With the SED fitting results, I find that massive galaxies present heavier dust extinctions, however, no correlation is found between the specific star formation rate and the dust extinction of the galaxies as some theories predict to explain the unexpected high number of bright galaxies detected by JWST at redshift z>10. Furthermore, I found the characteristic time of star formation to be mass and redshift-dependent: less massive and higher redshift galaxies form, on average, in a shorter time.
I also find an unexpectedly high number of galaxies exhibiting bursts of high star formation interspersed with periods of very low star formation. I characterize these star formation histories by finding an average duration of these low star formation rates to be on the order of 100 Myr, but with a large deviation. The result found tends to exclude the presence of star formation with negligible feedback in these galaxies.