Seeing sharper and deeper: JWST's first glimpse of the photometric and spectroscopic properties of galaxies in the epoch of reionisation

Abstract

We analyse the photometric and spectroscopic properties of four galaxies in the epoch of reionisation (EoR) within the SMACS 0723 JWST Early Release Observations field. Given the known spectroscopic redshifts of these sources, we investigated the accuracy with which photometric redshifts can be derived using NIRCam photometry alone, finding that F115W imaging is essential to distinguish between z~8 galaxies with high equivalent width (EW) [O III] λ5007 emission and z~10 Balmer break galaxies. We find that all four sources exhibit strong (\geq 0.6 mag) F356W-F444W colours, which sit at the extreme end of theoretical predictions from numerical simulations. We find that these galaxies deviate (by roughly 0.5 dex) from the local correlation between [O III] λ5007/Hβand [Ne III] λ3869/[O II], which is consistent with the predictions from simulations of high-redshift galaxies having elevated line excitation ratios. We measure the [O III] λ5007 rest-frame equivalent widths both directly from the spectroscopy, and indirectly as inferred from the strong F356W-F444W colours, finding large [O III] λ5007 EWs of 225-1740 Å. The [O III] λ5007 and HβEWs are consistent with those seen in extreme, intensely star-forming dwarf galaxies in the local Universe. Our structural analysis indicates that these galaxies are resolved, exhibiting irregular shapes with bright clumps. In line with the predictions from the FLARES hydrodynamic simulations, such intense star formation and extreme nebular conditions are likely the norm, rather than the exception, in the EoR.

17 pages, 9 figures. Now accepted and published in MNRAS

References in corpus (40)

• The EAGLE project: Simulating the evolution and assembly of galaxies and their environments
• The James Webb Space Telescope
• The EAGLE simulations of galaxy formation: calibration of subgrid physics and model variations
• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope I. Overview of the instrument and its capabilities
• Strong Nebular Line Ratios in the Spectra of z~2-3 Star-forming Galaxies: First Results from KBSS-MOSFIRE
• Strangulation as the primary mechanism for shutting down star formation in galaxies
• A Comprehensive Study on Galaxies at z~9-16 Found in the Early JWST Data: UV Luminosity Functions and Cosmic Star-Formation History at the Pre-Reionization Epoch
• The MOSFIRE Deep Evolution Field (MOSDEF) Survey: Rest-Frame Optical Spectroscopy for ~1500 H-Selected Galaxies at 1.37 < z < 3.8
• New fully empirical calibrations of strong-line metallicity indicators in star forming galaxies
• The mass evolution of the first galaxies: stellar mass functions and star formation rates at $4<z<7$ in the CANDELS GOODS-South field
• The chemical enrichment in the early Universe as probed by JWST via direct metallicity measurements at z~8
• Discovery and properties of ultra-high redshift galaxies ($9<z<12$) in the JWST ERO SMACS 0723 Field
• The JWST Early Release Observations
• The MOSDEF Survey: Excitation Properties of $z\sim 2.3$ Star-forming Galaxies
• The Near-Infrared Spectrograph (NIRSpec) on the James Webb Space Telescope II. Multi-object spectroscopy (MOS)
• Observational constraints on the merger history of galaxies since $z\approx 6$: Probabilistic galaxy pair counts in the CANDELS fields
• First look with JWST spectroscopy: $z\sim 8$ galaxies resemble local analogues
• High-precision Photometric Redshifts from Spitzer/IRAC: Extreme [3.6]-[4.5] Colors Identify Galaxies in the Redshift Range z~6.6-6.9
• The [OIII]$+$H$\beta$ Equivalent Width Distribution at z$\simeq$7: Implications for the Contribution of Galaxies to Reionization
• Panic! At the Disks: First Rest-frame Optical Observations of Galaxy Structure at $z>3$ with JWST in the SMACS 0723 Field
• First Light And Reionisation Epoch Simulations (FLARES) I: Environmental Dependence of High-Redshift Galaxy Evolution
• Diagnostics for PopIII galaxies and Direct Collapse Black Holes in the early universe
• Properties of the Multiphase Outflows in Local (Ultra)luminous Infrared Galaxies
• A massive, quiescent, population II galaxy at a redshift of 2.1
• A first look at the SMACS0723 JWST ERO: spectroscopic redshifts, stellar masses and star-formation histories
• First Light And Reionisation Epoch Simulations (FLARES) II: The Photometric Properties of High-Redshift Galaxies
• SDSS IV MaNGA -- Metallicity and ionisation parameter in local star-forming galaxies from Bayesian fitting to photoionisation models
• Probing Cosmic Dawn : Ages and Star Formation Histories of Candidate $z\ge$9 Galaxies
• Metallicity calibrations for diffuse ionised gas and low ionisation emission regions
• Semi-analytic forecasts for JWST -- VI. Simulated lightcones and galaxy clustering predictions
• Unscrambling the lensed galaxies in JWST images behind SMACS0723
• Interpreting high [O III]/Hbeta ratios with maturing starbursts
• First Light And Reionisation Epoch Simulations (FLARES) IV: The size evolution of galaxies at $z\ge 5$
• J2229+2725: an extremely low-metallicity dwarf compact star-forming galaxy with an exceptionally high [OIII]5007/[OII]3727 flux ratio of 53
• Assessing the sources of reionisation: a spectroscopic case study of a 30$\times$ lensed galaxy at $z\sim 5$ with Lyα, CIV, MgII, and [NeIII]
• The stellar metallicities of massive quiescent galaxies at 1.0 < z < 1.3 from KMOS+VANDELS
• The MOSDEF Survey: Neon as a Probe of ISM Physical Conditions at High Redshift
• The weak imprint of environment on the stellar populations of galaxies
• What drives the scatter of local star-forming galaxies in the BPT diagrams? A Machine Learning based analysis

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• UNCOVER: Illuminating the Early Universe -- JWST/NIRSpec Confirmation of $z>12$ Galaxies
• First Sample of H$\alpha$+[O III] $\lambda$5007 Line Emitters at $z>6$ Through JWST/NIRCam Slitless Spectroscopy: Physical Properties and Line Luminosity Functions
• EPOCHS IV: SED Modelling Assumptions and their impact on the Stellar Mass Function at 6.5 < z < 13.5 using PEARLS and public JWST observations
• Early Results from GLASS-JWST. XXI: Rapid assembly of a galaxy at z=6.23 revealed by its C/O abundance
• Dust attenuation law in JWST galaxies at z = 7-8
• CECILIA: The Faint Emission Line Spectrum of z~2-3 Star-forming Galaxies
• X-Shooting ULLYSES: Massive stars at low metallicity. IV. Spectral analysis methods and exemplary results for O stars
• Spatially resolved emission lines in galaxies at $4\le z<10$ from the JADES survey: evidence for enhanced central star formation
• Feedback and dynamical masses in high-$z$ galaxies: the advent of high-resolution NIRSpec spectroscopy
• Cloudy-Maraston: Integrating nebular continuum and line emission with the Maraston stellar population synthesis models
• SDSS-V LVM: Detectability of Wolf-Rayet stars and their He II ionizing flux in low-metallicity environments I. The weak-lined, early-type WN3 stars in the SMC