2024A&A...682A.182G

Mid-infrared (mid-IR) gas-phase molecular bands are powerful diagnostics of the warm interstellar medium. We report the James Webb Space Telescope detection of the CO v = 1 - 0 (4.4 - 5.0 μm) and H₂O ν₂ = 1 - 0 (5.0 - 7.8 μm) ro-vibrational bands, both in absorption, toward the “s2” core in the southwest nucleus of the merging galaxy VV 114 E. All ro-vibrational CO lines up to J_low = 33 (E_low ≈ 3000 K) are detected, as well as a forest of H₂O lines up to 13_0, 13_ (E_low ≈ 2600 K). The highest-excitation lines are blueshifted by ∼180 km s^–1 relative to the extended molecular cloud, which is traced by the rotational CO (J = 3 - 2) 346 GHz line observed with the Atacama Large Millimeter/submillimeter Array. The bands also show absorption in a low-velocity component (blueshifted by ≈30 km s^–1) with lower excitation. The analysis shows that the bands are observed against a continuum with an effective temperature of T_bck ∼ 550 K extinguished with $ \tau_{{6\,{\upmu}\mathrm{m}}}^{\mathrm{ext}}\sim 2.5{-}3 $ (A_k ∼ 6.9 - 8.3 mag). The high-excitation CO and H₂O lines are consistent with v = 0 thermalization with T_rot ≈ 450 K and column densities of N_CO ≈ (1.7 - 3.5)×10¹⁹ cm^–2 and N_H2O ≈ (1.5 - 3.0)×10¹⁹ cm^–2. Thermalization of the v = 0 levels of H₂O requires either an extreme density of n_H2 ≳ 10⁹ cm^–3, or radiative excitation by the mid-IR field in a very compact (< 1 pc) optically thick source emitting ∼10¹⁰ L_⊙. The latter alternative is favored, implying that the observed absorption probes the very early stages of a fully enshrouded active black hole (BH). On the basis of a simple model for BH growth and applying a lifetime constraint to the s2 core, an intermediate-mass BH (IMBH, M_BH ∼ 4.5 × 10⁴ M_⊙) accreting at super-Eddington rates is suggested, where the observed feedback has not yet been able to break through the natal cocoon.