The CON-quasar stage of IRAS 07251−0248 E

¹ Universidad de Alcalá, Departamento de Física y Matemáticas, Campus Universitario E-28871 Alcalá de Henares Madrid, Spain
² Instituto de Física Fundamental, CSIC Calle Serrano 123 E-28006 Madrid, Spain
³ Centro de Astrobiología (CAB), CSIC-INTA, Camino Bajo del Castillo s/n Villanueva de la Cañada E-28692 Madrid, Spain
⁴ George Mason University, Department of Physics & Astronomy, MS 3F3 4400 University Drive Fairfax VA 22030, USA

^★ Corresponding author: This email address is being protected from spambots. You need JavaScript enabled to view it.

Received: 5 August 2025
Accepted: 30 November 2025

Abstract

ALMA continuum measurements of the local ultra-luminous galaxy IRAS 07251−0248 E at 667 μm reveal an extremely compact (R ≲ 27 pc) and bright (T_B ≳ 200 K) nucleus with an absorbing foreground envelope and a surrounding (R ∼ 75 pc) disk or torus seen nearly face-on. The bright and unresolved nuclear emission implies large optical depths (τ_667 μm ≳ 0.5, corresponding to N_H ≳ 10²⁵ cm⁻²) of hot dust at ≳500 K. In addition, JWST observations of the source show strong mid-infrared (mid-IR) absorption in the ro-vibrational bands of H₂O ν₂ = 1 − 0 (5 − 7 μm) and of other species including CO, HCN, C₂H₂, CH₄, and CO₂, and Herschel/PACS observations exhibit strong and saturated absorption due to OH, H₂O, CH⁺, and CH. We propose a model in which the unresolved ALMA submillimeter and JWST mid-IR continua trace the same nuclear source, the former penetrating deep into the nucleus and the latter probing the nuclear photosphere. The continuum model, which includes trapping of photons (the “greenhouse” effect), indicates that the nuclear (R_h ≈ 13 pc) luminosity and luminosity surface density are ∼10¹² L_⊙ and Σ_bol ≈ 5 × 10⁸ L_⊙ pc⁻², arising from an active galactic nucleus (AGN) so buried that high-ionization lines are completely obscured. The observed mid-IR gas-phase molecular bands probe outflowing gas with velocities of ∼160 km s⁻¹ and are reproduced with the predicted T_dust profile, while the far-IR molecular absorption lines are generated in the surrounding thick disk or torus with τ_100 μm ∼ 10. We conclude that IRAS 07251−0248 harbors a compact obscured nucleus (CON) that hides an AGN currently emitting at quasar luminosity. While the observed outflow could be driven by radiation pressure, we favor the scenario of a (partially) energy-conserving hot bubble caught in a very early phase of the expulsion of the highly concentrated gas at the galactic nucleus.