First Insights into the ISM at $z&gt;8$ with JWST: Possible Physical Implications of a High [O III]$\mathbf{λ4363}$/[O III]$\mathbf{λ5007}$

Katz, Harley; Saxena, A.; Cameron, Alex; Carniani, Stefano; Bunker, Andrew J.; Arribas, S.; Bhatawdekar, Rachana; Bowler, R. A. A.; Boyett, Kristan; Cresci, G.; Curtis-Lake, Emma; D’Eugenio, Francesco; Kumari, Nimisha; Looser, Tobias J.; Übler, Hannah; Witstok, Joris

doi:10.48550/arxiv.2207.13693

Cited by 4 publications

(8 citation statements)

References 52 publications

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“…This possibly indicates that we enter at 𝑧 > 7 another epoch of galaxy formation, where galactic systems are out of equilibrium and evolve more stochastically. Consistent with this, other studies find high ionization, low metallicity and high pressure in the interstellar medium (ISM; Katz et al 2022;Schaerer et al 2022;Rhoads et al 2022;Trump et al 2022;Trussler et al 2022).…”

Section: Introductionsupporting

confidence: 71%

“…There are on-going efforts to expand upon this. Secondly, a recent analysis by Katz et al (2022) shows that the inclusion of high-mass X-ray binaries or a high cosmic ray background in addition to a young, low-metallicity stellar population can provide the additional heating necessary to explain the observed high [OIII]4364/[OIII]5007 ratio while remaining consistent with other observed line ratios. However, currently the nebular emission line modelling in Prospector does not extend to ionization parameters 𝑈 greater than −1.0 or high enough electron temperature (see Section 2.3), making it difficult to model extreme [OIII] line ratios.…”

Section: Caveats and Outlooksupporting

confidence: 61%

“…The resulting fluxes have already been published (Curti et al 2022, their Table 1) and are not repeated here. We remark that fitting each line individually does not change our conclusions, as reported in Katz et al (2022). The spectroscopic redshifts in this work are based on the emission-line velocities measured by .…”

Section: Nirspec Spectroscopymentioning

confidence: 57%

“…The cloudy modelling used a constant electron density and the highest ionization parameter in the grid is log(𝑈) = −1, making it difficult to model extreme [OIII] ratios (e.g. Ferland et al 2013;Katz et al 2022). Critically, the nebular emission is scaled by the number of ionizing photons predicted at each SSP age for the given SFH.…”

Section: Modelling Of the Spectro-photometric Datamentioning

confidence: 99%

“…These three objects have been discussed in several recent papers (e.g., Arellano-Córdova et al 2022;Carnall et al 2022;Curti et al 2022;Katz et al 2022;Rhoads et al 2022;Schaerer et al 2022;Trump et al 2022;Trussler et al 2022). The different studies rely on different measurement techniques, but also on different reduction and calibration pipelines, making comparisons difficult.…”

Section: Introductionmentioning

confidence: 99%

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JWST NIRCam+NIRSpec: Interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs

Tacchella¹,

Johnson²,

Robertson³

et al. 2022

Preprint

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We present an interstellar medium and stellar population analysis of three spectroscopically confirmed 𝑧 > 7 galaxies in the ERO JWST/NIRCam and JWST/NIRSpec data of the SMACS J0723.3-7327 cluster. We use the Bayesian spectral energy distribution (SED) fitting code Prospector with a flexible star-formation history (SFH), a variable dust attenuation law, and a self-consistent model of nebular emission (continuum and emission lines). Importantly, we self-consistently fit both the emission line fluxes from JWST/NIRSpec and the broad-band photometry from JWST/NIRCam, taking into account slit-loss effects. We find that these three 𝑧 = 7.6 − 8.5 galaxies (𝑀 ★ ≈ 10 8 𝑀 ) are young with rising SFHs and mass-weighted ages of 3 − 7 Myr, though we find indications for underlying older stellar populations. The inferred gas-phase metallicities broadly agree with the direct metallicity estimates from the auroral lines. The galaxy with the lowest gas-phase metallicity (Z gas = 0.06 Z ) has a steeply rising SFH, is very compact (< 0.2 kpc) and has a high star-formation rate surface density (Σ SFR ≈ 38 M yr −1 kpc −2 ), consistent with rapid gas accretion. The two other objects with higher gas-phase metallicity show more complex multi-component morphologies on kpc scales, indicating that their recent increase in star-formation rate is driven by mergers or internal, gravitational instabilities. We discuss effects of assuming different SFH priors or only fitting the photometric data. Our analysis highlights the strength and importance of combining JWST imaging and spectroscopy for fully assessing the nature of galaxies at the earliest epochs.

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Section: Introductionsupporting

confidence: 71%

Section: Caveats and Outlooksupporting

confidence: 61%

Section: Nirspec Spectroscopymentioning

confidence: 57%

Section: Modelling Of the Spectro-photometric Datamentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

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JWST NIRCam+NIRSpec: Interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs

Tacchella¹,

Johnson²,

Robertson³

et al. 2022

Preprint

Self Cite

View full text Add to dashboard Cite

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First look with JWST spectroscopy: Resemblance among z ∼ 8 galaxies and local analogs

Schaerer

Marques-Chaves

Barrufet

et al. 2022

A&A

105

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Deep images and near-IR spectra of galaxies in the field of the lensing cluster SMACS J0723.3−7327 were recently taken as part of the Early Release Observations (EROs) program of the James Webb Space Telescope (JWST). Among these, two NIRSpec spectra of galaxies, at z = 7.7 and at z = 8.5, were obtained, revealing, for the first time, the rest-frame optical emission line spectra of galaxies in the epoch of reionization, including the detection of the important [O iii]λ4363 auroral line (see JWST PR 2022-035). We present an analysis of the emission line properties of these galaxies, finding that these galaxies have a high excitation (as indicated by high, high equivalent widths, and other properties typical of low-metallicity star-forming galaxies. Using the direct method, we determined oxygen abundances of 12 + log(O/H) ≈ 7.9 in two z = 7.7 galaxies and a lower metallicity of 12 + log(O/H) ≈ 7.4−7.5 (∼5% solar) in the z = 8.5 galaxy using different strong line methods. More accurate metallicity determinations will require better data. With stellar masses estimated from spectral energy distribution (SED) fits, we find that the three galaxies lie close to or below the z ∼ 2 mass-metallicity relation. Overall, these first galaxy spectra at z ∼ 8 show a strong resemblance in their the emission line properties of galaxies in the epoch of reionization with those of relatively rare local analogs previously studied with the SDSS. Clearly, the first JWST observations demonstrate already the incredible power of spectroscopy to reveal the properties of galaxies in the early Universe.

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A lensed protocluster candidate at z = 7.66 identified in JWST observations of the galaxy cluster SMACS0723−7327

Laporte

Zitrin

Dole

et al. 2022

A&A

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Context. According to the current paradigm of galaxy formation, the first galaxies likely formed within large dark matter haloes. The fragmentation of these massive haloes led to the formation of galaxy protoclusters, which are usually composed of one to a few bright objects, surrounded by numerous fainter (and less massive) galaxies. These early structures could have played a major role in reionising the neutral hydrogen within the first billion years of the Universe, especially if their number density is significant. Aims. Taking advantage of the unprecedented sensitivity reached by the James Webb Space Telescope (JWST), galaxy protoclusters can now be identified and studied in increasing numbers beyond z ≥ 6. Characterising their contribution to the UV photon budget could supply new insights into the reionisation process. Methods. We analysed the first JWST dataset behind SMACS0723-7327 to search for protoclusters at z ≥ 6, combining the available spectroscopic and photometric data. We then compared our findings with semi-analytical models and simulations. Results. In addition to two bright galaxies (≤26.5 AB in F277W), separated by ∼11 and spectroscopically confirmed at z spec = 7.66, we identify six additional galaxies with similar colours within a θ ∼ 20 radius (corresponding to R∼ 60 − 90 kpc in the source plane). Using several methods, we estimate the mass of the dark matter halo of this protocluster as ∼3.3×10 11 M , accounting for magnification, consistent with various predictions. The physical properties of all protocluster members are also in excellent agreement with what has been previously found at lower redshifts: star formation main sequence and protocluster size. This detection adds to just a few protoclusters currently known in the first billion years of the universe. These z ≥ 7 galaxy protoclusters may play an important role in cosmic reionisation.

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First Insights into the ISM at $z>8$ with JWST: Possible Physical Implications of a High [O III]$\mathbf{λ4363}$/[O III]$\mathbf{λ5007}$

Cited by 4 publications

References 52 publications

JWST NIRCam+NIRSpec: Interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs

JWST NIRCam+NIRSpec: Interstellar medium and stellar populations of young galaxies with rising star formation and evolving gas reservoirs

First look with JWST spectroscopy: Resemblance among z ∼ 8 galaxies and local analogs

A lensed protocluster candidate at z = 7.66 identified in JWST observations of the galaxy cluster SMACS0723−7327

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