JWST/NIRSpec Spectroscopy of $z=7-9$ Star Forming Galaxies with CEERS: New Insight into Bright Ly$α$ Emitters in Ionized Bubbles

Abstract

We describe new JWST/NIRSpec observations of galaxies at 𝑧 7 taken as part of the CEERS survey of the EGS field. Previous observations of this area have revealed associations of Ly𝛼 emitters at redshifts (𝑧 = 7.5, 7.7, 8.7) where the IGM is thought mostly neutral, leading to suggestions that these systems are situated in large ionized bubbles. We identify 21 𝑧 7 galaxies with robust redshifts in the CEERS dataset, including 10 in the Ly𝛼 associations. Their spectra are indicative of very highly ionized and metal poor gas, with line ratios (O32 = 17.84 and Ne3O2 = 0.89) and metallicity (12 + log [O/H] = 7.84) that are rarely seen at lower redshifts. We find that the most extreme spectral properties are found in the six 𝑧 7 Ly𝛼 emitting galaxies in the sample. Each have hard ionizing spectra indicating that their visibility is likely enhanced by efficient ionizing photon production. Ly𝛼 velocity offsets are found to be very large ( 300 km s −1 ), likely also contributing to their detectability. We find that Ly𝛼 in 𝑧 7 galaxies is 6 − 12× weaker than in lower redshift samples with matched rest-frame optical spectral properties. If the bubbles around the Ly𝛼 emitters are relatively small ( 0.5 − 1 pMpc), we may expect such significant attenuation of Ly𝛼 in these ionized regions. We discuss several other effects that may contribute to weaker Ly𝛼 emission at 𝑧 7. Deep spectroscopy of fainter galaxies in the vicinity of the Ly𝛼 emitters will better characterize the physical scale of the ionized bubbles in this field.

CEERS Spectroscopic Confirmation of NIRCam-Selected z > 8 Galaxy Candidates with JWST/NIRSpec: Initial Characterization of their Properties

“…When the continuum is not well constrained (S/N < 2) from the fit, we estimate the underlying con- tinuum by correcting the slit-loss for the line emission (see Section 3.4) and subtracting the line contribution to the F444W photometry. We confirm that our EW measurements are consistent with the independent analysis and measurement for MPT-ID3, 23, and 24 presented in Tang et al (2023) within the errors. We do not detect [O ii] with S/N > 2 from any of the z spec sources.…”

“…This trend is different from the results at z ∼ 2 − 3 (black squares) but generally consistent with the model predictions (color-shaded regions), where the increasing trend is explained by the high ionization parameter in early galaxies (Hirschmann et al 2022;Hirschmann et al, in prep.). High O32 values of 10 have been reported from the composite spectrum for z ∼ 7.5 galaxies (Sanders et al 2023;Tang et al 2023), which also suggests the highly ionized ISM state in early galaxies. Second, we compare our measurements with recent JWST results and find that our NIRCamselected galaxies show the R3-M star distribution similar to the lensed galaxies at z = 7.5 − 9.5, ranging over the R3 values of ∼ 2-6 that are generally comparable or lower than those of the field galaxies at z = 5 − 7.…”

“…( 3)-( 6) are taken from Finkelstein et al (2022b). † These three galaxies have been also reported in Tang et al (2023).…”

“…The open blue pentagon and square indicate the observation mode of prism and Medium gratings, respectively. The green squares indicate other zspec confirmed galaxies taken from recent JWST studies showing both MUV and zspec measurements, from lensing cluster fields(Williams et al 2022;Roberts-Borsani et al 2022;Mascia et al 2023) and general fields(Tang et al 2023;Curtis- Lake et al 2022;Robertson et al 2022). The dashed vertical line presents the redshift limitation to detect the [O iii]5008 line with NIRSpec.…”

JADES NIRSpec Spectroscopy of GN-z11: Lyman-$α$ emission and possible enhanced nitrogen abundance in a $z=10.60$ luminous galaxy

“…Observations of Lyman-α emission and absorption provide strong constraints on how and when the diffuse gas in the IGM transitions from neu-with JWST is vastly increasing our knowledge in this area, both by detecting rest-frame optical lines of known Lyman-α emitters to derive systemic redshifts and details of nebular physical conditions, and by detecting Lyman-α further into the reionization epoch than has been possible from the ground (e.g. Tang et al 2023).…”