2018ApJ...859...35G

We report molecular gas observations of IRAS 20100-4156 and IRAS 03158+4227, two local ultraluminous infrared galaxies (ULIRGs) hosting some of the fastest and most massive molecular outflows known. Using Atacama Large Millimeter Array and Plateau de Bure Interferometer observations, we spatially resolve the CO (1-0) emission from the outflowing molecular gas in both and find maximum outflow velocities of v_max ∼ 1600 and ∼1700 km s^–1 for IRAS 20100-4156 and IRAS 03158+4227, respectively. We find total gas mass outflow rates of {dot}M_OF∼670 and ∼350 M_☉ yr^–1, respectively, corresponding to molecular gas depletion timescales τ_OF^dep∼11 and ∼16 Myr. This is nearly 3 times shorter than the depletion timescales implied by star formation, τ_SFR^dep∼33 and ∼46 Myr, respectively. To determine the outflow driving mechanism, we compare the starburst luminosity (L_*) and active galactic nucleus (AGN) luminosity (L_AGN) to the outflowing energy and momentum fluxes, using mid-infrared spectral decomposition to discern L_AGN. Comparison to other molecular outflows in ULIRGs reveals that outflow properties correlate similarly with L_* and L_IR as with L_AGN, indicating that AGN luminosity alone may not be a good tracer of feedback strength and that a combination of AGN and starburst activity may be driving the most powerful molecular outflows. We also detect the OH 1.667 GHz maser line from both sources and demonstrate its utility in detecting molecular outflows.