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The Dual Role of Starbursts and Active Galactic Nuclei in Driving Extreme Molecular Outflows

A. Gowardhan, H. W. W. Spoon, D. A. Riechers, E. GonzŠlez-Alfonso, D. Farrah, J. Fischer, J. Darling, C. Fergulio, J. Afonso, L. Bizzocchi

Abstract
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 ̇Ṁ~670 and ~350 M yr−1, respectively, corresponding to molecular gas depletion timescales τSFRdep~11 and ~16 Myr. This is nearly 3 times shorter than the depletion timescales implied by star formation, τSFRdep~33 and ~46 Myr, respectively. To determine the outflow driving mechanism, we compare the starburst luminosity (L*) and active galactic nucleus (AGN) luminosity (LAGN) to the outflowing energy and momentum fluxes, using mid-infrared spectral decomposition to discern LAGN. Comparison to other molecular outflows in ULIRGs reveals that outflow properties correlate similarly with L* and LIR as with LAGN, 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.

Keywords
galaxies: active; galaxies: evolution; galaxies: starburst; ISM: jets and outflows; ISM: molecules; techniques: interferometric

The Astronomical Journal
2018 May

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Instituto de Astrof√≠sica e Ci√™ncias do Espa√ßo Universidade do Porto Faculdade de Ciências da Universidade de Lisboa
Fundação para a Ciência e a Tecnologia COMPETE 2020 PORTUGAL 2020 União Europeia