TY - JOUR
T1 - Searching for Extremely Blue UV Continuum Slopes at z = 7-11 in JWST/NIRCam Imaging
T2 - Implications for Stellar Metallicity and Ionizing Photon Escape in Early Galaxies
AU - Topping, Michael W.
AU - Stark, Daniel P.
AU - Endsley, Ryan
AU - Plat, Adele
AU - Whitler, Lily
AU - Chen, Zuyi
AU - Charlot, Stéphane
N1 - Publisher Copyright:
© 2022. The Author(s). Published by the American Astronomical Society.
PY - 2022/12/1
Y1 - 2022/12/1
N2 - The ultraviolet (UV) continuum slope (β, where f λ ∝ λ β) 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 (β < −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 H ii 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 Extended Groth Strip field. We characterize UV slopes for a large sample of z ≃ 7-11 galaxies, finding a median of β = −2.0. Two lower luminosity (M UV ≃ −19.5) and lower stellar mass (6-10 × 107 M ⊙) systems exhibit extremely blue UV slopes (β = −2.9 to −3.1) and rest-optical photometry indicating weak nebular line emission. Each system is very compact (r e ≲ 260 pc) with very high star formation-rate surface densities. We model the spectral energy distributions (SEDs) with a suite of BEAGLE models with varying levels of ionizing photon escape. The SEDs cannot be reproduced with our fiducial (f esc,H II = 0) or alpha-enhanced (Z ⋆ < Z ISM) models. The combined blue UV slopes and weak nebular emission are best-fit by models with significant ionizing photon escape from H ii regions (f esc,H II = 0.5-0.8) and extremely low-metallicity massive stars (Z ⋆ = 0.01-0.06 Z ⊙). 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.
AB - The ultraviolet (UV) continuum slope (β, where f λ ∝ λ β) 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 (β < −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 H ii 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 Extended Groth Strip field. We characterize UV slopes for a large sample of z ≃ 7-11 galaxies, finding a median of β = −2.0. Two lower luminosity (M UV ≃ −19.5) and lower stellar mass (6-10 × 107 M ⊙) systems exhibit extremely blue UV slopes (β = −2.9 to −3.1) and rest-optical photometry indicating weak nebular line emission. Each system is very compact (r e ≲ 260 pc) with very high star formation-rate surface densities. We model the spectral energy distributions (SEDs) with a suite of BEAGLE models with varying levels of ionizing photon escape. The SEDs cannot be reproduced with our fiducial (f esc,H II = 0) or alpha-enhanced (Z ⋆ < Z ISM) models. The combined blue UV slopes and weak nebular emission are best-fit by models with significant ionizing photon escape from H ii regions (f esc,H II = 0.5-0.8) and extremely low-metallicity massive stars (Z ⋆ = 0.01-0.06 Z ⊙). 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.
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U2 - 10.3847/1538-4357/aca522
DO - 10.3847/1538-4357/aca522
M3 - Article
AN - SCOPUS:85144307148
SN - 0004-637X
VL - 941
JO - Astrophysical Journal
JF - Astrophysical Journal
IS - 2
M1 - 153
ER -