JWST/NIRSpec reference sample

We defined a new diagnostic, the Ly{alpha} damping parameter DLy{alpha}, to measure and quantify the net effect of Ly{alpha} emission strength, the HI fraction in the intergalactic medium, or the local HI column density for each source. The JWST-PRIMAL survey is based on the spectroscopic DAWN JWST Archive (DJA-Spec). We describe DJA-Spec in this paper, detailing the reduction methods, the post-processing steps, and basic analysis tools.

All the software, reduced spectra, and spectroscopically derived quantities and catalogs are made publicly available in dedicated repositories. We find that the fraction of galaxies showing strong integrated DLAs with NHI>10^21^cm^-2^ only increases slightly from ~60% at z~6 up to ~65-90% at z>8. Similarly, the prevalence and prominence of Ly{alpha} emission is found to increase with decreasing redshift, in qualitative agreement with previous observational results.

Strong Ly{alpha} emitters (LAEs) are predominantly found to be associated with low-metallicity and UV faint galaxies. By contrast, strong DLAs are observed in galaxies with a variety of intrinsic physical properties, but predominantly at high redshifts and low metallicities. Our results indicate that strong DLAs likely reflect a particular early assembly phase of reionization-era galaxies, at which point they are largely dominated by pristine HI gas accretion.

At z=8-10, this gas gradually cools and forms into stars that ionize their local surroundings, forming large ionized bubbles and producing strong observed Ly{alpha} emission at z<8.