Abstract
Context. The formation process of high-mass stars (>8 M⊙) is poorly constrained, particularly the effects of clump fragmentation creating multiple systems and the mechanism of mass accretion onto the cores. Aims. We study the fragmentation of dense gas clumps, and trace the circumstellar rotation and outflows by analyzing observations of the high-mass (~500 M⊙) star-forming region IRAS 23033+5951. Methods. Using the Northern Extended Millimeter Array (NOEMA) in three configurations and the IRAM 30 m single-dish telescope at 220 GHz, we probe the gas and dust emission at an angular resolution of ~0.45′′, corresponding to 1900 au. Results. In the millimeter (mm) continuum emission, we identify a protostellar cluster with at least four mm-sources, where three of them show a significantly higher peak intensity well above a signal-to-noise ratio of 100. Hierarchical fragmentation from large to small spatial scales is discussed. Two fragments are embedded in rotating structures and drive molecular outflows, traced by 13CO (2–1) emission. The velocity profiles across two of the cores are similar to Keplerian but are missing the highest-velocity components close to the center of rotation, which is a common phenomena from observations like these, and other rotation scenarios are not excluded entirely. Position–velocity diagrams suggest protostellar masses of ~6 and 19 M⊙. Rotational temperatures from fitting CH3CN (12K− 11K) spectra are used for estimating the gas temperature and thereby also the disk stability against gravitational fragmentation, utilizing Toomre’s Q parameter. Assuming that the candidate disk is in Keplerian rotation about the central stellar object and considering different disk inclination angles, we identify only one candidate disk as being unstable against gravitational instability caused by axisymmetric perturbations. Conclusions. The dominant sources cover different evolutionary stages within the same maternal gas clump. The appearance of rotation and outflows of the cores are similar to those found in low-mass star-forming regions.
Highlights
High-mass stars with masses exceeding 8 M contribute a significant fraction of luminosity of star clusters and galaxies and shape their visual appearance (e.g., Motte et al 2017)
We report the investigation of the high-mass star-forming region IRAS 23033+5951, listed as G110.0931
MMS1a, we present in Fig. 9 two PV diagrams for this core, with φ = 240◦ and φ = 290◦, where the second is motivated by the 13CO and CH3CN velocity gradient and the first is roughly perpendicular to the outflow axis and to the elongation of the cm emission
Summary
High-mass stars with masses exceeding 8 M contribute a significant fraction of luminosity of star clusters and galaxies and shape their visual appearance (e.g., Motte et al 2017). Beltrán & de Wit (2016) summarize the observational properties of accretion disks in HMSF which are embedded in flattened rotating structures (103–104 au) and thereby circumvent the radiation pressure problem for ongoing mass accretion This suggests that the formation scenario of high-mass objects is analogous to a scaled-up version of the low-mass star-forming process, that is, nonspherical mass accretion via circumstellar disks (e.g., Johnston et al 2013, 2015; Cesaroni et al 2014, 2017). The Northern Extended Millimeter Array (NOEMA) large program CORE (Beuther et al 2018) addresses open questions on fragmentation and disk formation during HMSF by investigating a sample of 20 high-mass star-forming regions at high spatial resolution in the cold dust and gas emission. The resulting cube has an rms noise of 2.15 mJy beam−1, with a synthesized beam of 0.8 × 0.67
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