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

Abstract

The ultraviolet (UV) continuum slope ($\beta$where$f_{\lambda }\propto {\lambda }^{\beta }$) of galaxies is sensitive to a variety of properties, from the metallicity and age of the stellar population to dust attenuation throughout the galaxy. Considerable attention has focused on identifying reionization-era galaxies with very blue UV slopes ($\beta <-3$). Not only do such systems provide a signpost of low-metallicity stars, but they also identify galaxies likely to leak ionizing photons from their HII regions as such blue UV slopes require the reddening effect of nebular continuum to be diminished. In this paper we present a search for reionization-era galaxies with very blue UV colors in recent JWST/NIRCam imaging of the EGS field. We characterize UV slopes for a large sample of$z\simeq 7-11$galaxies, finding a median of$\beta =-2.0$. Two lower luminosity (M${}_{\mathrm{UV}}\simeq -19.5$) and lower stellar mass (6-10$\times 10^7$M${}_{\odot }$) systems exhibit extremely blue UV slopes ($\beta =-2.9$to$-3.1$) and rest-optical photometry indicating weak nebular line emission. Each system is very compact (r${}_e\lesssim$260pc) with very high star-formation-rate surface densities. We model the SEDs with a suite of BEAGLE models with varying levels of ionizing photon escape. The SEDs cannot be reproduced with our fiducial (f${}_{\mathrm{esc},\mathrm{HII}}$=0) or alpha-enhanced (Z${}_{\star }<Z_{\mathrm{ISM}}$) models. The combined blue UV slopes and weak nebular emission are best-fit by models with significant ionizing photon escape from HII regions (f${}_{\mathrm{esc},\mathrm{HII}}$=0.5-0.8) and extremely low-metallicity massive stars (Z${}_{\star }$=0.01-0.06Z${}_{\odot }$). The discovery of these galaxies highlights the potential for JWST to identify large numbers of candidate Lyman Continuum leaking galaxies in the reionization-era and suggests low-metallicity stellar populations may be common in dwarf galaxies at $z>7$.

arXiv comment13 pages, 10 figures, 3 tables; Accepted to ApJ

References in corpus (64)

• Stellar population synthesis at the resolution of 2003
• The chemical composition of the Sun
• Galactic Stellar and Substellar Initial Mass Function
• MESA Isochrones and Stellar Tracks (MIST). I: Solar-Scaled Models
• CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey
• CANDELS: The Cosmic Assembly Near-infrared Deep Extragalactic Legacy Survey - The Hubble Space Telescope Observations, Imaging Data Products and Mosaics
• The propagation of uncertainties in stellar population synthesis modeling I: The relevance of uncertain aspects of stellar evolution and the IMF to the derived physical properties of galaxies
• UV Luminosity Functions at redshifts z~4 to z~10: 10000 Galaxies from HST Legacy Fields
• The propagation of uncertainties in stellar population synthesis modeling III: model calibration, comparison, and evaluation
• Binary Population and Spectral Synthesis Version 2.1: construction, observational verification and new results
• The Evolution of the Galaxy Rest-Frame Ultraviolet Luminosity Function Over the First Two Billion Years
• Stellar Population Inference with Prospector
• The All-wavelength Extended Groth Strip International Survey (AEGIS) Data Sets
• Reevaluating Old Stellar Populations
• Modelling and interpreting spectral energy distributions of galaxies with BEAGLE
• Reconciling the Stellar and Nebular Spectra of High Redshift Galaxies
• UV-Continuum Slopes of >4000 z~4-8 Galaxies from the HUDF/XDF, HUDF09, ERS, CANDELS-South, and CANDELS-North Fields
• Spectroscopic Confirmation of Three z-Dropout Galaxies at z = 6.844 - 7.213: Demographics of Lyman-Alpha Emission in z ~ 7 Galaxies
• Early star-forming galaxies and the reionization of the Universe
• Early results from GLASS-JWST. III: Galaxy candidates at z$\sim$9-15
• Modelling the nebular emission from primeval to present-day star-forming galaxies
• The Keck Lyman Continuum Spectroscopic Survey (KLCS): The Emergent Ionizing Spectrum of Galaxies at $z\sim 3$
• CANDELS: The Evolution of Galaxy Rest-Frame Ultraviolet Colors from z = 8 to 4
• The Characteristic Star Formation Histories of Galaxies at Redshifts z~2-7
• Evidence for Ubiquitous, High-EW Nebular Emission in z~7 Galaxies: Towards a Clean Measurement of the Specific Star Formation Rate using a Sample of Bright, Magnified Galaxies
• The Spectral Energy Distributions Of z~8 Galaxies From The IRAC Ultra Deep Fields: Emission Lines, Stellar Masses, And Specific Star Formation Rates At 650 Myr
• ALMA Spectroscopic Survey in the Hubble Ultra Deep Field: The Infrared Excess of UV-selected z=2-10 galaxies as a function of UV-continuum Slope and Stellar Mass
• Very blue UV-continuum slopes of low luminosity z~7 galaxies from WFC3/IR: Evidence for extremely low metallicities?
• Revealing Galaxy Candidates out to $z\sim 16$ with JWST Observations of the Lensing Cluster SMACS0723
• Z > 7 galaxies with red Spitzer/IRAC [3.6]-[4.5] colors in the full CANDELS data set: the brightest-known galaxies at Z ~ 7-9 and a probable spectroscopic confirmation at Z=7.48
• The HDUV Survey: A Revised Assessment of the Relationship between UV Slope and Dust Attenuation for High-Redshift Galaxies
• Predicted UV properties of very metal-poor starburst galaxies
• CANDELS: The Contribution of the Observed Galaxy Population to Cosmic Reionization
• A robust sample of galaxies at redshifts 6.0<z<8.7: stellar populations, star-formation rates and stellar masses
• Star formation rates and stellar masses of z=7-8 galaxies from IRAC observations of the WFC3/IR ERS and the HUDF field
• The spectral evolution of the first galaxies. II. Spectral signatures of Lyman continuum leakage from galaxies in the reionization epoch
• The Lyman Continuum Escape Survey: Ionizing Radiation from [O III]-Strong Sources at a Redshift of 3.1
• The UV continua and inferred stellar populations of galaxies at z ~ 7 - 9 revealed by the Hubble Ultra Deep Field 2012 campaign
• Direct Lyman continuum and Lyman-alpha escape observed at redshift 4
• The MOSDEF Survey: Direct-Method Metallicities and ISM Conditions at $z\sim 1.5-3.5$
• Stellar Populations of Lyman Alpha Emitters at z~6-7: Constraints on the Escape Fraction of Ionizing Photons from Galaxy Building Blocks
• The Low-Redshift Lyman Continuum Survey I: New, Diverse Local Lyman-Continuum Emitters
• The Low-Redshift Lyman Continuum Survey II: New Insights into LyC Diagnostics
• A critical analysis of the UV-continuum slopes of high-redshift galaxies; no evidence (yet) for extreme stellar populations at z > 6
• The [OIII]$+$H$\beta$ Equivalent Width Distribution at z$\simeq$7: Implications for the Contribution of Galaxies to Reionization
• Binary Stars Can Provide the "Missing Photons" Needed for Reionization
• The UV Properties of Star Forming Galaxies I: HST WFC3 Observations of Very-high Redshift Galaxies
• Constraints on the production and escape of ionizing radiation from the emission-line spectra of metal-poor star-forming galaxies
• The GREATS H$\beta$+[OIII] Luminosity Function and Galaxy Properties at $\mathbf{z}\sim 8$: Walking the Way of JWST
• The ALMA REBELS Survey: Specific Star-Formation Rates in the Reionization Era
• On the ages of bright galaxies $\sim 500$ Myr after the Big Bang: insights into star formation activity at $z\gtrsim 15$ with JWST
• The MOSDEF-LRIS Survey: The Interplay Between Massive Stars and Ionized Gas in High-Redshift Star-Forming Galaxies
• The Efficiency of Stellar Reionization: Effects of Rotation, Metallicity, and Initial Mass Function
• The Effects of Stellar Population and Gas Covering Fraction on the Emergent Lyman Alpha Emission of High-Redshift Galaxies
• The spectral evolution of the first Galaxies. III. Simulated James Webb Space Telescope spectra of reionization-epoch galaxies with Lyman continuum leakage
• UV Spectral-Slopes at $z=6-9$ in the Hubble Frontier Fields: Lack of Evidence for Unusual or Pop III Stellar Populations
• The unbiased measurement of UV spectral slopes in low luminosity galaxies at z=7
• JWST/NIRCam Observations of Stars and HII Regions in $z\simeq 6-8$ Galaxies: Properties of Star Forming Complexes on 150 pc Scales
• Chemical abundance scaling relations for multiple elements in z~2-3 star-forming galaxies
• The formation of UCDs and massive GCs: Quasar-like objects for testing for a variable stellar initial mass function (IMF)
• Predictions for the intrinsic UV continuum properties of star forming galaxies and the implications for inferring dust extinction
• Luminous Lyman-alpha Emitters with Very Blue UV-continuum Slopes at Redshift 5.7 <= z <= 6.6
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• Testing an indirect method for identifying galaxies with high levels of Lyman continuum leakage

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