Spectroscopic confirmation of a dust-obscured, possibly metal-rich dwarf galaxy at z ∼ 5

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(alpha )and H-beta,we derive that the galaxy has a dust extinction ranging from A(V) = 2.2(-0.6)(+0.5 )to AV = 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)(M/M)=8.17(-0.04)(+0.05 )or log(10)(M/M)=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+log(10)(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 starformation. 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).