Dusty Starbursts Masquerading as Ultra-high Redshift Galaxies in JWST CEERS Observations

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jats:titleAbstract</jats:title> jats:pLyman-break galaxy (LBG) candidates at jats:italicz</jats:italic> ≳ 10 are rapidly being identified in James Webb Space Telescope (JWST)/NIRCam observations. Due to the (redshifted) break produced by neutral hydrogen absorption of rest-frame UV photons, these sources are expected to drop out in the bluer filters while being well detected in redder filters. However, here we show that dust-enshrouded star-forming galaxies at lower redshifts (jats:italicz</jats:italic> ≲ 7) may also mimic the near-infrared (near-IR) colors of jats:italicz</jats:italic> > 10 LBGs, representing potential contaminants in LBG candidate samples. First, we analyze CEERS-DSFG-1, a NIRCam dropout undetected in the F115W and F150W filters but detected at longer wavelengths. Combining the JWST data with (sub)millimeter constraints, including deep NOEMA interferometric observations, we show that this source is a dusty star-forming galaxy (DSFG) at jats:italicz</jats:italic> ≈ 5.1. We also present a tentative 2.6jats:italicσ</jats:italic> SCUBA-2 detection at 850 jats:italicμ</jats:italic>m around a recently identified jats:italicz</jats:italic> ≈ 16 LBG candidate in the same field and show that, if the emission is real and associated with this candidate, the available photometry is consistent with a jats:italicz</jats:italic> ∼ 5 dusty galaxy with strong nebular emission lines despite its blue near-IR colors. Further observations on this candidate are imperative to mitigate the low confidence of this tentative submillimeter emission and its positional uncertainty. Our analysis shows that robust (sub)millimeter detections of NIRCam dropout galaxies likely imply jats:italicz</jats:italic> ∼ 4–6 redshift solutions, where the observed near-IR break would be the result of a strong rest-frame optical Balmer break combined with high dust attenuation and strong nebular line emission, rather than the rest-frame UV Lyman break. This provides evidence that DSFGs may contaminate searches for ultra-high redshift LBG candidates from JWST observations.</jats:p>

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Keywords
5109 Space Sciences, 5101 Astronomical Sciences, 51 Physical Sciences
Journal Title
Astrophysical Journal Letters
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Journal ISSN
2041-8205
2041-8213
Volume Title
943
Publisher
American Astronomical Society
Sponsorship
Space Telescope Science Institute (STScI) (JWST-ERS-1345)