High-z Galaxy Candidates in the COSMOS-Web Field

Seong Jin Kim^1*, Chih-Teng Ling¹, Tomotsugu Goto^1,2, Cossas K.-W. Wu^1,2, Katarzyna Malek³, William J. Pearson³, Agnieszka Pollo^3,4, Tetsuya Hashimoto⁵, Amos Y.-A. Chen², Ece Kilerci⁶, Simon C.-C. Ho^7,8,9,10, Yuri Uno⁵

¹Institute of Astronomy, National Tsing Hua University, Hsinchu, Taiwan
²Department of physics, National Tsing Hua University, Hsinchu, Taiwan
³National Centre for Nuclear Research, Pasteura 7, 02-093, Warszawa, Poland
⁴Faculty of Physics,, Jagiellonian University, Krakow, Poland
⁵Department of Physics, National Chung Hsing University, Taichung, Taiwan
⁶Faculaty of Engineering and Natural Science, Sabanci University, Istanbul, Turkey
⁷Research School of Astronomy and Astrophysics, The Australian National University, Canberra, Australia
⁸Centre for Astrophysics and Supercomputing, Swinburne University of Technology, Hawthorn, Australia
⁹OzGray, The Australian Research Council Centre of Excellence for Gravitational Wave Discovery, Hawthorn, Australia
¹⁰ASTRO3D, The Australian Research Council Centre of Excellence for All-sky Astrophysics in 3D, ACT 2661, Australia

* Presenter:Seong Jin Kim, email:seongini@gmail.com

With the advent of the James Webb Space Telescope (JWST), surprising aspects of star-forming galaxies (SFGs) in the early Universe have been uncovered. However, the discovery of massive galaxies at high-redshift remains limited due to the small field sizes of early JWST surveys. Using the JWST’s COSMOS-Web survey data, we searched for early galaxy candidates at z>10, the epoch of reionization (EoR) where the first galaxies were formed. We selected F115W dropout sources as candidates, characterized by detections in the F150W but not in F115W band, indicating a Lyman-alpha break. We examined photometric parameter spaces, visually inspected their NIRCam images, and conducted spectral energy distribution (SED) modeling. We found five candidates, and SED fitting suggests one candidate is remarkably massive (M∗ > 10¹⁰ M⊙). Other candidates have stellar masses around 10⁹ M⊙. The location of these galaxies on the M∗ vs SFR plane shows a trend similar to lower-redshift galaxies but with higher SFRs – possible main-sequence at z~10. Our estimated star-formation rate density suggests a steeper decline towards higher redshift compared to the pre-JWST estimates, consistent with earlier JWST findings. This work suggests that our galaxy candidates likely formed and evolved rapidly into massive (M∗ > 10⁹ M⊙) galaxies, although they require spectroscopic confirmation.

Keywords: JWST, High redshift galaxies, Reionization, Lyman-Break galaxies