2012A&A...548A..69N

Using Science Verification data from the Atacama Large Millimeter/Submillimeter Array (ALMA), we have identified and imaged five rotational transitions (J=5-4 and J=6-5) of the three silicon monoxide isotopologues ²⁸SiO v=0, 1, 2 and ²⁹SiO v=0 and ²⁸Si¹⁸O v=0 in the frequency range from 214 to 246 GHz towards the Orion BN/KL region. The emission of the ground-state ²⁸SiO, ²⁹SiO and ²⁸Si¹⁸O shows an extended bipolar shape in the northeast-southwest direction at the position of Radio Source I, indicating that these isotopologues trace an outflow (∼18km/s, PA∼50°, ∼5000AU in diameter) that is driven by this embedded high-mass young stellar object (YSO). Whereas on small scales (10-1000AU) the outflow from Source I has a well-ordered spatial and velocity structure, as probed by Very Long Baseline Interferometry (VLBI) imaging of SiO masers, the large scales (500-5000AU) probed by thermal SiO with ALMA reveal a complex structure and velocity field, most likely related to the effects of the environment of the BN/KL region on the outflow emanating from Source I. The emission of the vibrationally-excited species peaks at the position of Source I. This emission is compact and not resolved at an angular resolution of ∼1.5" (∼600AU at a distance of 420pc). 2D Gaussian fitting to individual velocity channels locates emission peaks within radii of 100AU, i.e. they trace the innermost part of the outflow. A narrow spectral profile and spatial distribution of the v=1 J=5-4 line similar to the masing v=1 J=1-0 transition, provide evidence for the most highly rotationally excited (frequency >200GHz) SiO maser emission associated with Source I known to date. The maser emission will enable studies of the Source I disk-outflow interface with future ALMA longest baselines.