MIDIS: MIRI uncovers Virgil, an extended source at z≃ 6.6 with the photometric properties of Little Red Dots

We present Virgil, a MIRI extremely red object (MERO) detected with the F1000W filter as part of the MIRI Deep Imaging Survey (MIDIS) observations of the Hubble Ultra Deep Field (HUDF). Virgil is a Lyman-α emitter (LAE) at z_spec = 6.6312± 0.0019 (from VLT/MUSE) with a rest-frame UV-to-optical spectral energy distribution (SED) typical of LAEs at similar redshifts. However, MIRI observations reveal an unexpected extremely red color at rest-frame near-infrared wavelengths, F444W - F1000W = 2.33 ± 0.06. Such steep rise in the near-infrared, completely missed without MIRI imaging, is poorly reproduced by models including only stellar populations and hints towards the presence of an Active Galactic Nucleus (AGN). Interestingly, the overall SED shape of Virgil resembles that of the recently discovered population of Little Red Dots (LRDs) but does not meet their compactness criterion: at rest-frame UV-optical wavelengths Virgil's morphology follows a 2D-Sérsic profile with average index n = 0.93^+0.85_-0.31 and r_e = 0.43 pkpc. Only at MIRI wavelengths Virgil is unresolved due to the coarser PSF. We also estimate a bolometric luminosity L_ bol = (8.4-11.1)× 10^44 erg s^-1 and a supermassive black hole mass M_ BH = (4-7)× 10^7  M_⊙ in agreement with recently reported values for LRDs. This discovery demonstrates the crucial importance of deep MIRI surveys to find AGN amongst high-z galaxies that otherwise would be completely missed and raises the question of how common Virgil-like objects could be in the early Universe.