GOALS-JWST: Resolved multi-phase molecular gas in IRAS 20551-4250 using JWST and ALMA

Studying the content and distribution of molecular gas (H2) provides key insights into how feedback from Active Galactic Nuclei (AGN) and star formation influences galaxy evolution, since molecular gas is the primary fuel for star formation. Ultra-Luminous Infrared Galaxies (ULIRGs) are ideal candidates to study how AGN and/or starbursts affect the interstellar medium due to their intense AGN and star forming activity. We present spatially-resolved multi-phase molecular gas study of IRAS20551-4250, a nearby (z = 0.0429) ULIRG, using JWST/MIRI-MRS and ALMA. Mid-infrared diagnostics do not rule out the presence of AGN in IRAS20551-4250. [O iii]λ5007 in VLT/MUSE data reveal ionised gas outflows with w₈₀[OIII] ~ 790 km s−1 and Ṁₒᵤₜ[OIII]<0.01 M⊙ yr−1. No outflows are observed in either molecular phases. JWST/MIRI-MRS data reveal several rotational transitions of warm H2 (T∼500 − 1400 K) within the central ∼4 × 4 kpc2 region. Excitation temperature maps suggest that the warm H2 is primarily heated by UV radiation from the central source. The CO-based cold molecular component dominates the molecular gas mass, accounting for >95 % of the total molecular gas mass. Warm H2 maps show two tidal tails and the velocity centroid maps show disturbed, non-rotational motions and a systematic gradient across the field-of-view, similar to that of ALMA CO-based cold molecular gas and consistent with a late-stage merger. Together, our analysis indicate that the molecular gas composition in IRAS20551-4250 is consistent with ongoing star formation in the host galaxy and the outflows observed in ionised gas phase appear insufficient to expel the molecular gas or quench ongoing star formation.