Outflow Structure and Velocity Field of Orion Source I: ALMA Imaging of SiO Isotopologue Maser and Thermal Emission

Abstract

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 (~18 km/s, P.A. ~50deg, ~5000 AU in diameter) that is driven by this embedded high-mass young stellar object (YSO). Whereas on small scales (10-1000 AU) 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 (500-5000 AU) 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" (~600 AU at a distance of 420 pc). 2-D Gaussian fitting to individual velocity channels locates emission peaks within radii of 100 AU, 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 > 200 GHz) 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.

Accepted to A&A, 11 pages, 13 figures

References in corpus (1)

• Imaging the Ionized Disk of the High-Mass Protostar Orion-I

Cited by in corpus (16)

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• ALMA Observations of Orion Source I at 350 and 660 GHz
• Dynamical Evidence for a Magnetocentrifugal Wind from a 20 Msun Binary Young Stellar Object
• Hot Molecular Circumstellar Disk around Massive Protostar Orion Source I
• Orion Source I's disk is salty
• Cloud-cloud Collision in the Galactic Center 50 km s${}^{-1}$ Molecular Cloud
• Extended warm gas in Orion KL as probed by methyl cyanide
• ALMA Imaging of Millimeter/Submillimeter Continuum Emission in Orion KL
• Observations of Orion Source I Disk and Outflow Interface
• Magnetic Field Structure of Orion Source I
• ALMA Observation of the 658 GHz Vibrationally Excited H${}_2$O Maser in Orion KL Source I
• ALMA band 8 continuum emission from Orion Source I
• Structure of the Source I disk in Orion-KL
• A spectroscopic survey of Orion KL between 41.5 and 50 GHz
• Extremely high excitation SiO lines in disk-outflow system in Orion Source I
• An ionized outflow in Orion-KL source I?