An infrared-luminous merger with two bipolar molecular outflows: ALMA and SMA observations of NGC3256

Journal article, 2014

We report Atacama Large Millimeter/sub-millimeter Array and Submillimeter Array observations of the infrared-luminous merger NGC3256, the most luminous galaxy within z = 0.01. Both of the two merger nuclei separated by 5 '' (0.8 kpc) have a molecular gas concentration, a nuclear disk, with Sigma(mol) > 10(3) M-circle dot pc(-2). The northern nucleus is more massive and is surrounded by molecular spiral arms. Its nuclear disk is face-on, while the southern nuclear disk is almost edge-on. The high-velocity molecular gas in the system can be resolved into two molecular outflows from the two nuclei. The one from the northern nucleus is part of a starburst-driven superwind seen nearly pole-on. Its maximum velocity is > 750 km s(-1) and its mass outflow rate is > 60M(circle dot) yr(-1) for a conversion factor X-CO = N-H2 / ICO(1-0) of 1 x 10(20) cm(-2) (K km s(-1))(-1). The molecular outflow from the southern nucleus is a highly collimated bipolar jet seen nearly edge-on. Its line-of-sight velocity increases with distance, out to 300 pc from the nucleus, to the maximum de-projected velocity of similar to 2000 km s(-1) for the estimated inclination and greater than or similar to 1000 km s(-1) taking into account the uncertainty. Its mass outflow rate is estimated to be > 50M(circle dot) yr(-1) for the same XCO. This southern outflow has indications of being driven by a bipolar radio jet from an active galactic nucleus that recently weakened. The sum of these outflow rates, although subject to the uncertainty in the molecular mass estimate, either exceeds or compares to the total star formation rate. The feedback from nuclear activity through molecular outflows is therefore significant in the gas consumption, and hence evolution, of this system.