Massive star formation and feedback in W49A: The source of our Galaxy's most luminous water maser outflow

Abstract

We present high spatial resolution mid-IR images of the ring of UCHII regions in W49A obtained at Gemini North, allowing us to identify the driving source of its powerful H2O maser outflow. These data also confirm our previous report that several radio sources in the ring are undetected in the mid-IR because they are embedded deep inside the cloud core. We locate the source of the water maser outflow at the position of the compact mid-IR peak of source G (source G:IRS1). This IR source is not coincident with any identified compact radio continuum source, but is coincident with a hot molecular core, so we propose that G:IRS1 is a hot core driving an outflow analogous to the wide-angle bipolar outflow in OMC-1. G:IRS1 is at the origin of a larger bipolar cavity and CO outflow. The water maser outflow is orthogonal to the bipolar CO cavity, so the masers probably reside near its waist in the cavity walls. Models of the IR emission require a massive protostar of 45Msun, 3e5Lsun, and an effective envelope accretion rate of 1e-3Msun/yr. Feedback from the central star could potentially drive the H2O maser outflow, but it has insufficient radiative momentum to have driven the large-scale CO outflow, requiring that this massive star had an active accretion disk over the past 10^4 yr. Combined with the spatialy resolved morphology in IR images, G:IRS1 in W49 provides compelling evidence for a massive protostar that formed by accreting from a disk, accompanied by a bipolar outflow.

14 pages, MNRAS accepted

References in corpus (5)

• Fragmentation of Massive Protostellar Disks
• A Near-Infrared and X-ray Study of W49B: A Wind Cavity Explosion
• A Census of the Carina Nebula -- II. Energy Budget and Global Properties of the Nebulosity
• An equatorial wind from the massive young stellar object S140 IRS 1
• Hard X-rays from Ultra-Compact HII Regions in W49A

Cited by in corpus (16)

• Explosive Outflows Powered by the Decay of Non-Hierarchical Multiple Systems of Massive Stars: Orion BN/KL
• CHIMPS: the ${}^{13}$CO/C${}^{18}$O (J=3-2) Heterodyne Inner Milky Way Plane Survey
• The ALMA View of the OMC1 Explosion in Orion
• MUSCLE W49 : A Multi-Scale Continuum and Line Exploration of the Most Luminous Star Formation Region in the Milky Way. I. Data and The Mass Structure of the Giant Molecular Cloud
• The Orion Fingers: Near-IR Adaptive Optics Imaging of an Explosive Protostellar Outflow
• Collective outflow from a small multiple stellar system
• The G305 star forming complex: Wide-Area molecular mapping of NH3 and H2O masers
• Extended warm and dense gas towards W49A: starburst conditions in our Galaxy?
• The Orion fingers: Near-IR spectral imaging of an explosive outflow
• Time-Variable Radio Recombination Line Emission in W49A
• The Orion fingers: H${}_2$ temperatures and excitation in an explosive outflow
• Extremely Energetic Outflow and Decelerated Expansion in W49N
• Flux Density Variations at 3.6 cm in the Massive Star-Forming Region W49A
• Surveying the Giant HII Regions of the Milky Way with SOFIA: III. W49A
• Formation of Orion Fingers
• The Outcome of the Protoplanetary Disk of Very Massive Stars