Ultrahigh-redshift or closer-by, dust-obscured galaxies?

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Context. The James Webb Space Telescope (JWST) is revolutionizing our understanding of the Universe by unveiling faint, near-infrared dropouts previously beyond our reach, ranging from exceptionally dusty sources to galaxies up to redshift z ∼ 14. Aims. In this paper, we identify F200W-dropout objects in the Cosmic Evolution Early Release Science (CEERS) survey that are absent from existing catalogs. Our selection method can effectively identify obscured low-mass (logM * /M ⊙ ≤ 9) objects at z ≤ 6, massive dust-rich sources up to z ∼ 12, and ultrahigh-redshift ( z > 15) candidates. Our goal is to uncover promising targets for further studies using deep mid-infrared imaging and/or spectroscopic follow-ups. Methods. We utilize two photometric catalogs optimized for detecting faint, red objects. Primarily relying on NIRCam photometry from the latest CEERS data release and supplementing with mid-infrared/(sub)millimeter data when available, our analysis pipeline combines multiple SED-fitting codes, star formation histories, and the novel CosMix tool for astronomical stacking to maximize available photometric information. Results. Our work highlights three 2 < z < 3 dusty dwarf galaxies that have higher masses compared to the typical dusty dwarfs previously identified in CEERS. Additionally, we reveal five faint sources with a significant probability of lying above z > 15, with best-fit masses compatible with Λ cold dark matter and a standard baryon-to-star conversion efficiency. We exploit these candidates to compute the z ∼ 17 UV luminosity function, finding estimates in good agreement with other similar studies. Their bimodal redshift probability distributions suggest they could also be z < 1.5 dwarf galaxies with extreme dust extinction. We also identify a strong line emitter galaxy at z ∼ 5 mimicking the near-infrared emission of a z ∼ 13 galaxy. Conclusions. Our sample holds promising candidates for future follow-ups. Confirming ultrahigh-redshift galaxies or lower-redshift dusty dwarfs will offer valuable insights into early galaxy formation, evolution with their central black holes and the nature of dark matter, and/or cosmic dust production mechanisms in low-mass galaxies, and will help us to understand degeneracies and contamination in high-redshift object searches.

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