Hitting the slopes: a spectroscopic view of UV continuum slopes of galaxies reveals a reddening at z > 9.5

ABSTRACT The ultraviolet (UV) continuum slope of galaxies, $\beta$, is a powerful diagnostic of the metallicity and ages of stars, nebular gas properties, dust content, and the escape of Lyman continuum (LyC) photons. In this study, we present $\beta$ measurements for 395 spectroscopically confirmed galaxies at $5 \lt z \lt 14.3$ selected primarily from JADES, using high-quality JWST (James Webb Space Telescope) NIRSpec/PRISM spectra. We find a median $\beta = -2.15$, finding a mild increase in blueness of $\beta$ with increasing redshift and fainter UV magnitudes. Interestingly, we find evidence for reddening of the average $\beta$ at $z \gt 9.5$, deviating from the trend observed at $z \lt 9.5$. Using…

• NS
  National Science Foundation
• NA
  National Aeronautics and Space Administration

  Awards: 5-03127, NAS 5-03127, NAS5-02015
• ES
  Entomological Society of America
• UO
  University of Arizona

  Award: NAS5-02015
• CS
  Communal Studies Association
• ST
  Space Telescope Science Institute

  Awards: NAS5-02015, 5-03127, NAS 5-03127
• UR
  UK Research and Innovation

  Awards: 101040227, PID2021-127718NB-I00
• EC
  European Commission

  Awards: 101164796, ST/W001438/1, 789056, 695671, 101040227
• MD
  Ministerio de Ciencia e Innovación

  Award: PID2021-127718NB-I00
• NA
  National Academy of Sciences

  Award: 5–03127
• SA
  Science and Technology Facilities Council

  Awards: ST/W001438/1, PID2021-127718NB-I00, NAS5-02015, 695671
• AE
  Agencia Estatal de Investigación
• HE
  H2020 European Research Council

  Awards: 101164796, 101040227