Molecular line emission in NGC 1068 imaged with ALMA:I. An AGN-driven outflow in the dense molecular gas

Aims: We investigate the fueling and the feedback of starformation and nuclear activity in NGC 1068, a nearby(D = 14 Mpc) Seyfert 2 barred galaxy, by analyzing the distribution andkinematics of the molecular gas in the disk. We aim to understand if andhow gas accretion can self-regulate. Methods: We have used theAtacama Large Millimeter Array (ALMA) to map the emission of a set ofdense molecular gas (n(H2) ≃ 105 - 6cm-3) tracers (CO(3-2), CO(6-5), HCN(4-3),HCO+(4-3), and CS(7-6)) and their underlying continuumemission in the central r ~ 2 kpc of NGC 1068 withspatial resolutions ~0.3″ - 0.5″ (~20-35 pc for the assumeddistance of D = 14 Mpc). Results: The sensitivity and spatialresolution of ALMA give an unprecedented detailed view of thedistribution and kinematics of the dense molecular gas (n(H2)≥ 105 - 6cm-3) in NGC 1068.Molecular line and dust continuum emissions are detected from a r ~ 200pc off-centered circumnuclear disk (CND), from the 2.6 kpc-diameter barregion, and from the r ~ 1.3 kpc starburst (SB) ring. Most of theemission in HCO+, HCN, and CS stems from the CND. Molecularline ratios show dramatic order-of-magnitude changes inside the CND thatare correlated with the UV/X-ray illumination by the active galacticnucleus (AGN), betraying ongoing feedback. We used the dust continuumfluxes measured by ALMA together with NIR/MIR data to constrain theproperties of the putative torus using CLUMPY models and found a torusradius of 20+6-10pc. The Fourier decomposition ofthe gas velocity field indicates that rotation is perturbed by an inwardradial flow in the SB ring and the bar region. However, the gaskinematics from r ~ 50 pc out to r ~ 400 pc reveal a massive(Mmol~ 2.7+0.9-1.2 ×107 M⊙) outflow in all molecular tracers. Thetight correlation between the ionized gas outflow, the radio jet, andthe occurrence of outward motions in the disk suggests that the outflowis AGN driven. Conclusions: The molecular outflow is likelylaunched when the ionization cone of the narrow line region sweeps thenuclear disk. The outflow rate estimated in the CND, dM/dt~63+21-37 M⊙ yr-1, is anorder of magnitude higher than the star formation rate at these radii,confirming that the outflow is AGN driven. The power of the AGN is ableto account for the estimated momentum and kinetic luminosity of theoutflow. The CND mass load rate of the CND outflow implies a very shortgas depletion timescale of ≤1 Myr. The CND gas reservoir is likelyreplenished on longer timescales by efficient gas inflow from the outerdisk.Based on observations carried out with ALMA in Cycle 0