James Webb Space Telescope Feed Post

JWST/NIRSpec Spectroscopy of z=7-9 Star Forming Galaxies with CEERS: New Insight into Bright Lyα Emitters in Ionized Bubbles Published: 1/17/2023 8:34:32 PM Updated: 9/22/2023 5:04:36 AM

Paper abstract: We describe new JWST/NIRSpec observations of galaxies at z\gtrsim7 takenfrom the CEERS survey. Previous observations of this area have revealedassociations of Ly\alpha emitters at redshifts (z=7.5, 7.7, 8.7) wherethe intergalactic medium (IGM) is thought to be mostly neutral, leading tosuggestions that these systems are situated in large ionized bubbles. Weidentify 21 z\gtrsim7 galaxies with robust redshifts in the CEERS dataset,including 10 in the Ly\alpha associations. Their spectra are indicative ofvery highly ionized and metal poor gas, with line ratios (O32 =17.84 andNe3O2 =0.89, linear scale) and metallicity (12+\log{(\rm{O/H})}=7.84) thatare rarely seen at lower redshifts. We find that the most extreme spectralproperties are found in the six z\gtrsim7 Ly\alpha emitters in the sample.Each has a hard ionizing spectrum indicating that their visibility is likelyenhanced by efficient ionizing photon production. Ly\alpha velocity offsetsare found to be very large (\gtrsim300 km s^{-1}), likely also contributingto their detectability. We find that Ly\alpha in z\gtrsim7 galaxies is6-12\times weaker than in lower redshift samples with matched rest-opticalspectral properties. If the bubbles around the Ly\alpha emitters arerelatively small (<~0.5-1 pMpc), we may expect such significantattenuation of Ly\alpha in these ionized regions. We discuss several othereffects that may contribute to weaker Ly\alpha emission at z\gtrsim7. Deepspectroscopy of fainter galaxies in the vicinity of the Ly\alpha emitterswill better characterize the physical scale of the ionized bubbles in thisfield.