JADES: Physical properties of Ly$\alpha$ and non-Ly$\alpha$ emitters at z ~ 4.8-9.6

TL;DR

This study analyzes the physical properties of Ly$ extalpha$ and non-Ly$ extalpha$ emitters at redshifts 4.8 to 9.6 using JWST/NIRSpec spectra, revealing differences in ionization, line ratios, and potential AGN influence at early cosmic times.

Contribution

It provides the first detailed comparison of physical properties of LAEs and non-LAEs at z~4.8-9.6 using JWST data, highlighting differences in ionization and emission line ratios.

Findings

LAEs show higher [OIII]/[OII] ratios than non-LAEs at z<6.3.

LAEs have large EW([OIII]) (>1000 Å) across all redshifts.

Active galactic nuclei may dominate the emission line spectra.

Abstract

We investigate the physical properties of Lyman-alpha emitters (LAEs) and non-Lyman-alpha emitters (non-LAEs) at z$\sim$4.8--9.6 via a stacking analysis of 253 JWST/NIRSpec spectra of galaxies observed as part of the JWST Advanced Deep Extragalactic Survey (JADES). We identify a sample of 42 LAEs with the equivalent width of Ly$\alpha$ $\gtrsim$20\AA and a sample of 211 non-LAEs, divide each sample further via the median redshift of the LAEs (z~6.3), and create composite spectra using the low and medium resolution spectra from NIRSpec. We estimate physical quantities such as dust extinction, UV continuum slope $\beta$, electron temperatures, ionization parameter, escape fraction of Ly$\alpha$ and Lyman Continuum, and the photon production rate for each bin/stack. The existing dust-extinction laws do not appear to be valid at these epochs. The emission line ratio analyses show that active galactic nuclei might dominate all sub-samples, irrespective of Ly$\alpha$ emission. LAEs show much higher [OIII]/[OII] and low [OII]/H$\delta$ at z$\lesssim$6.3 compared to non-LAEs, but these line ratios are not sufficient to distinguish the two populations at z$>$6.3. However, the LAEs samples show large EW([OIII]4959, 5007) ($>$1000\AA) compared to the non-LAEs sample at all redshifts. CIV/Ly$\alpha$ and CIV/CIII] for LAE population at z$\lesssim$6.3 is $\sim$a factor of 5 larger than that for LAE population at z$>$6.3. The ionizing radiation for LAEs is hard, as revealed from several diagnostics, including CIV detection, high [OIII]/[OII] ($>$8), and large values of $\xi^{\star}_{ion}$.