James Webb Space Telescope Feed Post

Harvard ADS: JWST/NIRSpec Observations of Lyman α Emission in Star-forming Galaxies at 6.5 ≲ z ≲ 13

Paper abstract: We present an analysis of JWST Lya spectroscopy of z ? 6.5 galaxies, using observations in the public archive covering galaxies in four independent fields: Great Observatories Origins Deep Survey (GOODS)-N, GOODS-S, A2744, and the Extended Groth Strip (EGS). We measure the Lya emission line properties for a sample of 210 z ? 6.5–13 galaxies, with redshifts confirmed independently of Lya in all cases. We present three new detections of Lya emission in JWST spectra, including a large equivalent width (EW; =143 Å) Lya emitter (LAE) with strong C IV emission (EW = 21 Å) at z = 7.1 in GOODS-N. We measure the redshift-dependent Lya EW distribution across our sample. We find that strong Lya emission (EW > 25 Å) becomes increasingly rare at earlier epochs, suggesting that the transmission of Lya photons decreases by 4× between z ? 5 and z ? 9. We describe potential implications for the intergalactic medium neutral fraction. There is significant field-to-field variance in the LAE fraction. In contrast to the three other fields, the EGS shows no evidence for reduced transmission of Lya photons at z ? 7–8, suggesting a significantly ionized sight line may be present in the field. We use available NIRCam grism observations from the First Reionization Epoch Spectroscopically Complete Observations survey to characterize overdensities on large scales around known LAEs in the GOODS fields. The strongest overdensities appear linked with extremely strong Lya detections (EW > 50 Å) in most cases. Future Lya spectroscopy with JWST has the potential to constrain the size of ionized regions around early galaxy overdensities, providing a new probe of the reionization process.