Can AGN Feedback Quench Star Formation in Mergers? Constraints from Multiwavelength SED Fitting and ALMA Observations of their Molecular Gas

Major galaxy mergers trigger intense starbursts that are eventually quenched, with AGN feedback proposed as the key mechanism. The dual AGN phase at <10 kpc separations—when both SMBHs grow simultaneously—may mark the critical transition from peak activity to quenching. We present studies addressing the conditions and evidence for AGN feedback in merging systems. Multiwavelength SED analysis of 72 Swift-BAT AGN in mergers reveals that late-stage coalescence exhibits 5× enhanced star formation alongside 2.4× higher AGN luminosities and 2.8× increased obscuration, indicating peak SMBH accretion coincident with peak starburst activity. High-resolution ALMA CO observations show that molecular gas becomes concentrated within SMBH spheres of influence as separations decrease, making fuel reservoirs potentially vulnerable to feedback-driven removal. However, ALMA ACA 12CO(2–1) observations of 18 GOALS (U)LIRGs reveal no clear signatures of strong molecular outflows. Identified outflow candidates have velocities below escape velocities, suggesting gas remains gravitationally bound. Mass outflow rates and AGN contributions to bolometric luminosity support a scenario where feedback is primarily stellar-driven rather than AGN-driven. These results suggest that despite favorable conditions—concentrated gas and active SMBHs—AGN feedback may not yet dominate in these systems, raising questions about when and how AGN-driven quenching occurs.