JWST/NIRCam Observations of Stars and HII Regions in $z\simeq 6-8$ Galaxies: Properties of Star Forming Complexes on 150 pc Scales

Abstract

The onset of the {\it JWST}-era provides a much-improved opportunity to characterize the resolved structure of early star forming systems. Previous {\it Spitzer} observations of $z\gtrsim 6$ galaxies revealed the presence of old stars and luminous HII regions (via [OIII]+H$\beta$ emission), but the poor resolution stunted our ability to map their locations with respect to the star forming regions identified in the rest-UV. In this paper, we investigate the internal structure of 12 of the most luminous $z\simeq 6-8$ galaxies in the EGS field observed with recent {\it JWST}/NIRCam imaging. The systems appear clumpy in the rest-UV, with more than half of the light coming from $\simeq 10^7$ to 10${}^9$ M${}_{\odot }$ star forming complexes that are $\simeq 150$ - 480 pc in size. The clumps tend to be dominated by young stars (median = 36 Myr), but we also find large variations in clump ages within individual galaxies. The [OIII]+H$\beta$ EW varies significantly across individual galaxies (reflecting differences in stellar and gas properties), but the HII regions largely track the UV-bright complexes. Perhaps surprisingly, the rest-optical continuum is just as clumpy as the UV, and we do not find older (and redder) nuclear stellar components that were previously undetected or faint in the UV. The majority of the stellar mass in bright $6<z<8$ galaxies appears to be contained in the $\gtrsim 150$ pc-scale clumpy star forming complexes, reflecting the very active phase of assembly that is common in reionization-era galaxies.

main text 12 pages, 7 figures; accepted for publication by MNRAS

References in corpus (36)

• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• Stellar Population Inference with Prospector
• Formation and Dynamical Evolution of Multiple Stellar Generations in Globular Clusters
• The All-wavelength Extended Groth Strip International Survey (AEGIS) Data Sets
• The Evolution of Galaxy Structure over Cosmic Time
• Modelling the nebular emission from primeval to present-day star-forming galaxies
• Imfit: A Fast, Flexible New Program for Astronomical Image Fitting
• Galaxy growth in a massive halo in the first billion years of cosmic history
• Clumpy Galaxies in CANDELS. I. The Definition of UV Clumps and the Fraction of Clumpy Galaxies at 0.5<z<3
• Galaxy Formation and Reionization: Key Unknowns and Expected Breakthroughs by the James Webb Space Telescope
• On the Stellar Populations of Galaxies at z=9-11: The Growth of Metals and Stellar Mass at Early Times
• Reionization Era Bright Emission Line Survey: Selection and Characterization of Luminous Interstellar Medium Reservoirs in the z>6.5 Universe
• Paving the way for the JWST: witnessing globular cluster formation at z>3
• Observational constraints on the merger history of galaxies since $z\approx 6$: Probabilistic galaxy pair counts in the CANDELS fields
• Resolved spectroscopy of gravitationally lensed galaxies: global dynamics and star-forming clumps on ~100pc scales
• The [OIII]$+$H$\beta$ Equivalent Width Distribution at z$\simeq$7: Implications for the Contribution of Galaxies to Reionization
• I Zw 18 revisited with HST/ACS and Cepheids: New Distance and Age
• The GREATS H$\beta$+[OIII] Luminosity Function and Galaxy Properties at $\mathbf{z}\sim 8$: Walking the Way of JWST
• The sizes of $z\sim 6-8$ lensed galaxies from the Hubble Frontier Fields Abell 2744 data
• ALMA reveals metals yet no dust within multiple components in CR7
• The ALMA REBELS Survey: Specific Star-Formation Rates in the Reionization Era
• Dual constraints with ALMA: new [O III] 88 $\mu$m and dust-continuum observations reveal the ISM conditions of luminous LBGs at $z\sim 7$
• Probing Cosmic Dawn : Ages and Star Formation Histories of Candidate $z\ge$9 Galaxies
• Early results from GLASS-JWST. V: the first rest-frame optical size-luminosity relation of galaxies at $z>7$
• Near-Infrared Spectroscopy of Galaxies During Reionization: Measuring CIII] in a Galaxy at $\mathbf{z}=7.5$
• The discovery of rest-frame UV colour gradients and a diversity of dust morphologies in bright z ~ 7 Lyman-break galaxies
• ALMA reveals extended cool gas and hot ionized outflows in a typical star-forming galaxy at $z=7.13$
• High Equivalent Width of Hα+[N II] Emission in z~8 Lyman-break Galaxies from IRAC 5.8μm Observations: Evidence for Efficient Lyman-continuum Photon production in the Epoch of Re-ionization
• Sizes of Lensed Lower-luminosity z=4-8 Galaxies from the Hubble Frontier Field Program
• Rest-frame UV spectroscopy of extreme [OIII] emitters at $1.3<z<3.7$: Toward a high-redshift UV reference sample for JWST
• The Prevalence of Galaxy Overdensities Around UV-Luminous Lyman $\alpha$ Emitters in the Epoch of Reionization
• Searching for z > 6.5 Analogs Near the Peak of Cosmic Star Formation
• Sub-parsec resolution cosmological simulations of star-forming clumps at high redshift with feedback of individual stars
• Star-forming clumps in the Lyman Alpha Reference Sample of galaxies -- I. Photometric analysis and clumpiness
• Stellar populations and star formation histories of the most extreme [OIII] emitters at $z=1.3-3.7$
• The Nearby and Extremely Metal-Poor Galaxy CGCG 269-049

Cited by in corpus (27)

• The James Webb Space Telescope Mission
• The brightest galaxies at Cosmic Dawn
• A JWST/NIRCam Study of Key Contributors to Reionization: The Star-forming and Ionizing Properties of UV-faint $z\sim 7-8$ Galaxies
• JADES Imaging of GN-z11: Revealing the Morphology and Environment of a Luminous Galaxy 430 Myr After the Big Bang
• EIGER II. first spectroscopic characterisation of the young stars and ionised gas associated with strong H$\beta$ and [OIII] line-emission in galaxies at z=5-7 with JWST
• A Candidate of a Least-Massive Black Hole at the First 1.1 Billion Years of the Universe
• Searching for Extremely Blue UV Continuum Slopes at $z=7-11$ in JWST/NIRCam Imaging: Implications for Stellar Metallicity and Ionizing Photon Escape in Early Galaxies
• JWST early Universe observations and ΛCDM cosmology
• UNCOVER: Illuminating the Early Universe -- JWST/NIRSpec Confirmation of $z>12$ Galaxies
• The MillenniumTNG Project: The galaxy population at $z\ge 8$
• Spatially Resolved Properties of High Redshift Galaxies in the SMACS0723 JWST ERO Field
• JWST reveals a possible $z\sim 11$ galaxy merger in triply-lensed MACS0647$-$JD
• Cosmological Model Tests with JWST
• RELICS: Small-scale Star Formation in Lensed Galaxies at $z=6-10$
• Euclid: Early Release Observations -- Globular clusters in the Fornax galaxy cluster, from dwarf galaxies to the intracluster field
• Testing CCC+TL Cosmology with Observed BAO Features
• Ly-alpha emission in low-redshift most metal-deficient compact star-forming galaxies
• Effects of feedback on galaxies in the VELA simulations: elongation, clumps and compaction
• Spectroscopy of CASSOWARY gravitationally-lensed galaxies in SDSS: characterisation of an extremely bright reionization-era analog at $z=1.42$
• First Light And Reionisation Epoch Simulations (FLARES) XII: The consequences of star-dust geometry on galaxies in the EoR
• A SPectroscopic survey of biased halos In the Reionization Era (ASPIRE): JWST Discovers an Overdensity around a Metal Absorption-selected Galaxy at $z\sim 5.5$
• A MUSE/VLT spatially resolved study of the emission structure of Green Pea galaxies
• GA-NIFS: Dissecting the multiple sub-structures and probing their complex interactions in the \Lyalpha emitter galaxy CR7 at z = 6.6 with JWST/NIRSpec
• COLIBRE: calibrating subgrid feedback in cosmological simulations that include a cold gas phase
• Radiation-driven dusty outflows from early galaxies
• Extended Enriched Gas in a Multi-Galaxy Merger at Redshift 6.7
• Evolution of Size, Mass, and Density of Galaxies Since Cosmic Dawn