The Astrophysical Journal (Jan 2024)

Unveiling the Distant Universe: Characterizing z ≥ 9 Galaxies in the First Epoch of COSMOS-Web

  • Maximilien Franco,
  • Hollis B. Akins,
  • Caitlin M. Casey,
  • Steven L. Finkelstein,
  • Marko Shuntov,
  • Katherine Chworowsky,
  • Andreas L. Faisst,
  • Seiji Fujimoto,
  • Olivier Ilbert,
  • Anton M. Koekemoer,
  • Daizhong Liu,
  • Christopher C. Lovell,
  • Claudia Maraston,
  • Henry Joy McCracken,
  • Jed McKinney,
  • Brant E. Robertson,
  • Micaela B. Bagley,
  • Jaclyn B. Champagne,
  • Olivia R. Cooper,
  • Xuheng Ding,
  • Nicole E. Drakos,
  • Andrea Enia,
  • Steven Gillman,
  • Ghassem Gozaliasl,
  • Santosh Harish,
  • Christopher C. Hayward,
  • Michaela Hirschmann,
  • Shuowen Jin,
  • Jeyhan S. Kartaltepe,
  • Vasily Kokorev,
  • Clotilde Laigle,
  • Arianna S. Long,
  • Georgios Magdis,
  • Guillaume Mahler,
  • Crystal L. Martin,
  • Richard Massey,
  • Bahram Mobasher,
  • Louise Paquereau,
  • Alvio Renzini,
  • Jason Rhodes,
  • R. Michael Rich,
  • Kartik Sheth,
  • John D. Silverman,
  • Martin Sparre,
  • Margherita Talia,
  • Benny Trakhtenbrot,
  • Francesco Valentino,
  • Aswin P. Vijayan,
  • Stephen M. Wilkins,
  • Lilan Yang,
  • Jorge A. Zavala

DOI
https://doi.org/10.3847/1538-4357/ad5e6a
Journal volume & issue
Vol. 973, no. 1
p. 23

Abstract

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We report the identification of 15 galaxy candidates at z ≥ 9 using the initial COSMOS-Web JWST observations over 77 arcmin ^2 through four Near Infrared Camera filters (F115W, F150W, F277W, and F444W) with an overlap with the Mid-Infrared Imager (F770W) of 8.7 arcmin ^2 . We fit the sample using several publicly available spectral energy distribution (SED) fitting and photometric redshift codes and determine their redshifts between z = 9.3 and z = 10.9 (〈 z 〉 = 10.0), UV magnitudes between M _UV = −21.2 and −19.5 (with 〈 M _UV 〉 = −20.2), and rest-frame UV slopes (〈 β 〉 = −2.4). These galaxies are, on average, more luminous than most z ≥ 9 candidates discovered by JWST so far in the literature, while exhibiting similar blue colors in their rest-frame UV. The rest-frame UV slopes derived from SED fitting are blue ( β ∼ [−2.0, −2.7]) without reaching extremely blue values as reported in other recent studies at these redshifts. The blue color is consistent with models that suggest the underlying stellar population is not yet fully enriched in metals like similarly luminous galaxies in the lower-redshift Universe. The derived stellar masses with $\langle {\mathrm{log}}_{10}($ M _⋆ / M _⊙ )〉 ≈ 8–9 are not in tension with the standard Lambda cold dark matter (ΛCDM) model, and our measurement of the volume density of such UV-luminous galaxies aligns well with previously measured values presented in the literature at z ∼ 9–10. Our sample of galaxies, although compact, is significantly resolved.

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