Early Results from GLASS-JWST. XVI. Discovering a Bluer z ∼ 4-7 Universe through UV Slopes

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  • Themiya Nanayakkara
  • Karl Glazebrook
  • Colin Jacobs
  • Andrea Bonchi
  • Marco Castellano
  • Adriano Fontana
  • Emiliano Merlin
  • Takahiro Morishita
  • Diego Paris
  • Michele Trenti
  • Tommaso Treu
  • Antonello Calabrò
  • Kristan Boyett
  • Marusa Bradac
  • Nicha Leethochawalit
  • Danilo Marchesini
  • Paola Santini
  • Eros Vanzella
  • Benedetta Vulcani
  • Xin Wang
  • Lilian Yang

We use the GLASS-JWST Early Release Science NIRCam parallel observations to provide a first view of the UV continuum properties of NIRCam/F444W selected galaxies at 4 < z < 7. By combining multiwavelength NIRCam observations, we constrain the UV continuum slope for a sample of 401 galaxies with stringent quality controls. We find that >99% of the galaxies are blue star-forming galaxies with very low levels of dust (Av β ∼ 0.01 ± 0.33). We find no statistically significant correlation for UV slope with redshift or UV magnitude. However, we find that in general galaxies at higher redshifts and fainter UV magnitudes have steeper UV slopes. We find a statistically significant correlation for UV slope with stellar mass, with galaxies with higher stellar mass showing shallower UV slopes. Individual fits to some of our galaxies reach the bluest UV slopes of β ∼ −3.1 allowed by stellar population models used in this analysis. Therefore, it is likely that stellar population models with a higher amount of Lyman continuum leakage, active galactic nucleus effects, and/or Population III contributions are required to accurately reproduce the rest-UV and optical properties of some of our bluest galaxies. This dust-free early view confirms that our current cosmological understanding of gradual mass + dust buildup of galaxies with cosmic time is largely accurate to describe the ∼0.7-1.5 Gyr age window of the universe. The abundance of a large population of UV faint dust-poor systems may point to a dominance of low-mass galaxies at z > 6 playing a vital role in cosmic reionization.

Original languageEnglish
Article numberL26
JournalAstrophysical Journal Letters
Volume947
Issue number2
Number of pages9
ISSN2041-8205
DOIs
Publication statusPublished - 2023

Bibliographical note

Funding Information:
This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program JWST-ERS-1342. We acknowledge financial support from NASA through grant JWST-ERS-1324. T.N., K.G., and C.J. acknowledge support from Australian Research Council Laureate Fellowship FL180100060. M.B. acknowledges support from the Slovenian national research agency ARRS through grant N1-0238. C.M. acknowledges support by the VILLUM FONDEN under grant 37459. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant DNRF140. This project made use of astropy (Astropy Collaboration et al. ), matplotlib (Hunter ), and pandas (pandas development team ).

Funding Information:
This work is based on observations made with the NASA/ESA/CSA James Webb Space Telescope. The data were obtained from the Mikulski Archive for Space Telescopes at the Space Telescope Science Institute, which is operated by the Association of Universities for Research in Astronomy, Inc., under NASA contract NAS 5-03127 for JWST. These observations are associated with program JWST-ERS-1342. We acknowledge financial support from NASA through grant JWST-ERS-1324. T.N., K.G., and C.J. acknowledge support from Australian Research Council Laureate Fellowship FL180100060. M.B. acknowledges support from the Slovenian national research agency ARRS through grant N1-0238. C.M. acknowledges support by the VILLUM FONDEN under grant 37459. The Cosmic Dawn Center (DAWN) is funded by the Danish National Research Foundation under grant DNRF140. This project made use of astropy (Astropy Collaboration et al. 2018), matplotlib (Hunter 2007), and pandas (pandas development team 2020).

Publisher Copyright:
© 2023. The Author(s). Published by the American Astronomical Society.

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