2025A&A...693L..18B

We present the first spectroscopic confirmation of a dust-obscured dwarf galaxy, CEERS-14821. The analysis was performed by combining JWST NIRCam broadband photometry and NIRSpec/PRISM spectroscopic data. From the detection of multiple rest-frame optical lines, we derive that CEERS-14821 is located at z = 4.883 ± 0.003. Moreover, from a secure detection of the H_α and H_β, we derive that the galaxy has a dust extinction ranging from $ A_{V}=2.2_{-0.6}^{+0.5} $ to $ A_{V}=3.4_{-0.9}^{+0.7} $, depending on the assumed reddening law. This value is extremely large given that we estimated a low stellar mass, that is, $ \log_{10}(\mathrm{M}/\mathrm{M}_{\odot})=8.17_{-0.04}^{+0.05} $ or $ \log_{10}(\mathrm{M}/\mathrm{M}_{\odot})=8.65_{-0.05}^{+0.06} $, based on two different dust extinction laws. Moreover, the combination of different metallicity tracers and the spectro-photometric fit suggests that the galaxy may also be metal-rich, with 12 + log₁₀(O/H)> 8.3, but a low metallicity value cannot be totally ruled out. The high metallicity value would be above the expectation based on the mass-metallicity relation. Both metallicity estimations are above the expectations based on the fundamental mass-metallicity relation since CEERS-14821 is going through a burst of star formation. The constraints on a possible active galactic nucleus presence are limited and loose, but they point towards a possible non-dominant contribution (f_AGN < 0.5 with respect to the total dust luminosity). Based on the rest-frame optical images, this source has a size compatible with galaxies of similar stellar masses and at similar redshifts. Finally, CEERS-14821 may be part of a larger galaxy overdensity, but there are no other galaxies closely interacting with it (within 30 Mpc).