ALMA reveals a compact and massive molecular outflow driven by the young AGN in a nearby ULIRG

The ultraluminous infrared galaxy F13451 + 1232 is an e xcellent e xample of a galaxy merger in the early stages of active galactic nucleus (AGN) activity, a phase in which AGN-dri ven outflo ws are expected to be particularly important. Ho we ver, pre vious observ ations have determined that the mass outflo w rates of the warm ionized and neutral gas phases in F13451 + 1232 are relatively modest, and there has been no robust detection of molecular outflows. Using high-spatial resolution Atacama Large Millimeter/submillimeter Array CO(1-0) observations, we detect a kiloparsec-scale circumnuclear disc, as well as extended ( r ∼440 pc), intermediate-velocity (300 < | v| < 400 km s -1 ) cold molecular gas emission that cannot be explained by rotational disc motions. If interpreted as AGN-driven outflows, the mass outflow rates associated with this intermediate- velocity gas are relatively modest ( M out = 22-27 M ⊙yr -1 ); ho we ver, we also detect a compact ( r out < 120 pc), high-velocity (400 < v < 680 km s -1 ) cold molecular outflow near the primary nucleus of F13451 + 1232, which carries an order of magnitude more mass ( M out ∼230 M ⊙yr -1 ) than (and several times the kinetic power of) the previously detected warmer phases. Moreo v er, the similar spatial scales of this compact outflow and the radio structure indicate that it is likely accelerated by the small- scale ( r ∼130 pc) AGN jet in the primary nucleus of F13451 + 1232. Considering the compactness of the nuclear outflow and intermediate-velocity non-rotating gas that we detect, we argue that high-spatial resolution observations are necessary to properly quantify the properties of AGN-driven outflows and their impacts on host galaxies.