Abstract
Context. Increasing evidence suggests that, similar to their low-mass counterparts, high-mass stars form through a disk-mediated accretion process. At the same time, formation of high-mass stars still necessitates high accretion rates, and hence, high gas densities, which in turn can cause disks to become unstable against gravitational fragmentation. Aims. We study the kinematics and fragmentation of the disk around the high-mass star forming region AFGL 2591-VLA 3 which was hypothesized to be fragmenting based on the observations that show multiple outflow directions. Methods. We use a new set of high-resolution (0′′.19) IRAM/NOEMA observations at 843 μm towards VLA 3 which allow us to resolve its disk, characterize the fragmentation, and study its kinematics. In addition to the 843 μm continuum emission, our spectral setup targets warm dense gas and outflow tracers such as HCN, HC3N and SO2, as well as vibrationally excited HCN lines. Results. The high resolution continuum and line emission maps reveal multiple fragments with subsolar masses within the inner ~1000 AU of VLA 3. Furthermore, the velocity field of the inner disk observed at 843 μm shows a similar behavior to that of the larger scale velocity field studied in the CORE project at 1.37 mm. Conclusions. We present the first observational evidence for disk fragmentation towards AFGL 2591-VLA 3, a source that was thought to be a single high-mass core. While the fragments themselves are low-mass, the rotation of the disk is dominated by the protostar with a mass of 10.3 ± 1.8 M⊙. These data also show that NOEMA Band 4 can obtain the highest currently achievable spatial resolution at (sub-)mm wavelengths in observations of strong northern sources.
Highlights
High-mass stars (M > 8 M ) regulate the dynamical and chemical evolution of the interstellar medium (ISM), yet the exact routes that lead to their formation are still under debate
This study reveals that a Toomre-unstable disk fragments on scales below 500 AU, where each fragment hosts its own smaller scale accretion disk that is best resolved in the synthetic Atacama Large Millimeter/submillimeter Array (ALMA) observations reaching an angular resolution of ∼80 mas at a distance of 800 pc
We present a new set of high spatial resolution NOrthern Extended Millimeter Array (NOEMA) observations as an extension of the CORE large program carried out at 843 μm towards Very Large Array (VLA) 3
Summary
High-mass stars (M > 8 M ) regulate the dynamical and chemical evolution of the interstellar medium (ISM), yet the exact routes that lead to their formation are still under debate. In order to address the open questions in high-mass star formation studies, namely the underlying physics and chemistry during formation and fragmentation of disks along with the infall and outflow processes, we observed 20 high-mass star forming regions (HMSFRs) at 1.37 mm within the framework of the IRAM NOEMA large program “CORE2” (Beuther et al 2018). AFGL 2591 is one of the most luminous HMSFRs with L ∼ 2 × 105 L at a distance of 3.33 kpc (Rygl et al 2012) It is in the direction of the Cygnus X star-forming complex and it is associated with a large-scale (>1 ∼ 1 pc), high-velocity (∆V ≥ 30 km s−1) molecular outflow reported by Bally & Lada (1983).
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