Kavli Affiliate: Roberto Maiolino
| Summary:
We targeted with deep NOEMA observations the [CII]158$μ$m emission of three JWST-discovered AGN at z>6. Two of them have the typical features of Little Red Dots (LRDs), while the third one is a blue, extended, Type I AGN. We do not significantly detect [CII] emission or dust continuum in any of the targets, even after stacking. The resulting [CII] luminosity upper limits, $log (L_[CII]/L_odot)<7.77-8.1$, lie $sim2σ$ below the values expected from the [CII]-SFR relation, and we explore different scenarios to explain the lack of [CII]. We obtained upper limits on the gas masses of $log (M_gas/M_odot)<9.26-9.59$ corresponding to $log( M_dust/M_odot)<5.68-6.55$ assuming a metallicity dependent dust to gas ratio. Using the continuum non-detections (rms $sim 16-25 ~μJy$) together with JWST/MIRI constraints, we performed a revised SED-fitting decomposition, resulting in stellar masses up to $sim 2$ dex lower than previously reported, and implying $0.03lesssim M_BH/M_*lesssim0.7$. For the two LRDs, the SED is well reproduced by stellar emission in the rest-frame UV, while the rising rest-frame optical slope, flattening toward the near-infrared, is consistent with emission from a Type I AGN partially obscured along the polar direction with $E(B-V)_rm polarsimeq 1$, in agreement with attenuation derived from the broad lines Balmer decrement. This decomposition demonstrates that a relatively standard AGN configuration can reproduce the SEDs of the two LRDs, without invoking more exotic scenarios. Finally, we investigate the positions of the three sources in the $IRX-β_UV$ plane, finding that they lie in a parameter space where galaxies are typically characterized by patchy dust distributions. Our analysis highlights the importance of millimeter constraints to characterize the different physical properties of high-z AGN.
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