A NIRCam-dark galaxy detected with the MIRI/F1000W filter in the MIDIS/JADES Hubble Ultra Deep Field

We report the discovery of Cerberus, an extremely red object detected with the MIRI Deep Imaging Survey (MIDIS) observations in the F1000W filter of the Hubble Ultra Deep Field. The object is detected at S/N 6, with F1000W 27 mag, and it is extremely faint in both the NIRCam data gathered by the JWST Advanced Deep Extragalactic Survey, JADES, with  30.5 mag 5σ upper limits in individual bands, as well as in the MIDIS F560W ultra deep data (∼29 mag, 5σ). Analyzing the spectral energy distribution built with individual (low S/N) optical-to-mid-infrared filters and (S/N 5) stacks, we discuss the possible nature of this red NIRCam-dark source using a battery of codes. We discard the possibility of Cerberus being a Solar System body based on the <0.016" proper motion in the 1-year apart JADES and MIDIS observations. A sub-stellar Galactic nature is deemed unlikely, given that the Cerberus' relatively flat NIRCam-to-NIRCam and very red NIRCam-to-MIRI flux ratios are not consistent with any brown dwarf model. The extragalactic nature of Cerberus offers 3 possibilities: (1) A z∼0.4 galaxy with strong emission from polycyclic aromatic hydrocarbons; the very low inferred stellar mass, M_⋆=10^5-6 M_⊙, makes this possibility highly improbable. (2) A dusty galaxy at z∼4 with an inferred stellar mass M_⋆∼10^8 M_⊙. (3) A galaxy with observational properties similar to those of the reddest little red dots discovered around z∼7, but Cerberus lying at z∼15, presenting a spectral energy distribution in the rest-frame optical dominated by emission from a dusty torus or a dusty starburst.