Observations of high-order multiplicity in a high-mass stellar protocluster.pdf
Nature Astronomy | Volume 8 | April 2024 | 472–481 472 nature astronomy Article https://doi.org/10.1038/s41550-023-02181-9 Observations of high-order multiplicity in a  high-mass stellar protocluster Shanghuo Li    1  , Patricio Sanhueza2,3, Henrik Beuther    1,  Huei-Ru Vivien Chen    4, Rolf Kuiper    5, Fernando A. Olguin    4,  Ralph E. Pudritz    6, Ian W. Stephens    7, Qizhou Zhang    8,  Fumitaka Nakamura    2,3, Xing Lu    9, Rajika L. Kuruwita10, Takeshi Sakai    11,  Thomas Henning    1, Kotomi Taniguchi    2 & Fei Li12 The dominant mechanism forming multiple stellar systems in the  high-mass regime (M* ≳ 8 M⊙) remained unknown because direct imaging of  multiple protostellar systems at early phases of high-mass star formation  is very challenging. High-mass stars are expected to form in clustered  environments containing binaries and higher-order multiplicity systems. So  far only a few high-mass protobinary systems, and no definitive higher-order  multiples, have been detected. Here we report the discovery of one  quintuple, one quadruple, one triple and four binary protostellar systems  simultaneously forming in a single high-mass protocluster, G333.23–0.06,  using Atacama Large Millimeter/submillimeter Array high-resolution  observations. We present a new example of a group of gravitationally  bound binary and higher-order multiples during their early formation  phases in a protocluster. This provides the clearest direct measurement  of the initial configuration of primordial high-order multiple systems,  with implications for the in situ multiplicity and its origin. We find that the  binary and higher-order multiple systems, and their parent cores, show no  obvious sign of disk-like kinematic structure. We conclude that the observed  fragmentation into binary and higher-order multiple systems can be  explained by core fragmentation, indicating its crucial role in establishing  the multiplicity during high-mass star cluster formation. High-mass stars in the Milky Way are overwhelmingly (>80%; refs. 1–6)  found in binaries or higher-order multiplicity systems that play a key  role in governing cluster dynamics and stellar evolution7,8. However,  it is yet unclear whether they are predominantly formed from in situ  fragmentation at various scales (for example, disks9,10, cores11,12 or  filaments13) or subsequent stellar capture in clusters14 because direct  measurements of their initial configuration and properties at the early  phases of cluster formation have been unattainable15–27. Received: 20 October 2023 Accepted: 11 December 2023 Published online: 15 January 2024  Check for updates 1Max Planck Institute for Astronomy, Heidelberg, Germany. 2National Astronomical Observatory of Japan, National Institutes of Natural Sciences, Tokyo,  Japan. 3Department of Astronomical Science, School of Physical Science, SOKENDAI (The Graduate University for Advanced Studies), Tokyo, Japan.  4Institute of Astronomy and Department of Physics, National Tsing Hua University, Hsinchu, Taiwan. 5Faculty of Physics, University of Duisburg-Essen,  Duisburg, Germany. 6Origins Institute and Department of Physics and Astronomy, McMaster University, Hamilton, Ontario, Canada. 7Department of Earth,  Environment, and Physics, Worcester State University, Worcester, MA, USA. 8Center for Astrophysics, Harvard & Smithsonian, Cambridge, MA, USA.  9Shanghai Astronomical Observatory, Chinese Academy of Sciences, Shanghai, P.R. China. 10Heidelberg Institute for Theoretical Studies, Heidelberg,  Germany. 11Graduate School of Informatics and Engineering, The University of Electro-Communications, Tokyo, Japan. 12School of Astronomy and Space  Science, Nanjing University, Nanjing, P.R. China.   e-mail: shanghuo.li@gmail.com Nature Astronomy | Volume 8 | April 2024 | 472–481 473 Article https://doi.org/10.1038/s41550-023-02181-9 the simulation of multiple star formation via core fragmentation29.  The ambient gas masses (Mamb) of these multiple systems range from  0.19 to 1.47 M⊙ on the basis of the thermal dust emission (Methods).  These masses are regarded as lower limits because the observations  suffered from missing flux in the interferometer data. We focus primar- ily on the multiple systems that are embedded in a single dense core  (typical radius of ∼2,100 AU; Fig. 1). The quintuple system consists of  a small group of condensations (C1–C4–C5–C16), which is tightly con- nected as seen in dust continuum emission, and a condensation (C3)  slightly separated. That is nevertheless part of the original parental core   (Fig. 1). The quadruple system includes two binary configurations  (C10–C14 and C8–C17), and the triple system composes three slightly  separated condensations (C6, C12 and C26). The binary systems are  C11–C29, C22–C38, C39–C42 and C35–C40. We report the direct imaging of one quintuple, one quadruple, one  triple and four binary systems in the high-mass protocluster G333.23– 0.06 (hereafter G333) using Atacama Large Millimeter/submillim- eter Array (ALMA) long-baseline observations (Fig. 1 and Extended  Data Fig. 1). These binary and higher-order systems are detected in  the high-resolution (angular resolution of θ ≈ 0.05″, equivalent to  260 AU at the source distance of 5.2 kpc; ref. 28) 1.3 mm dust continuum  image. The detected condensations have radii between 153 and 678 AU   (Table 1). We refer to both binary and higher-order systems simply as  multiple systems in what follows, and we only make an explicit distinc- tion between the two when necessary. The projected separations of these multiple systems are between  327 and 1,406 AU, with a mean value of 731 AU (Extended Data Fig. 2),  in good agreement with the typical projected separation of 700 AU in  6 5 4 3 2 1 dec. (ICRS) Continuum flux density (mJy per beam) 12’’ 16’’ 20’’ 51.8 s 51.6 s 51.4 s 51.2 s RA (ICRS) 51.0 s 50.8 s 16 h 19 m 50.6 s X  condensation ALMA (high-resolution) ALMA (high-resolution) ALMA (low-resolution) ALMA (high-resolution) ALMA (high-resolution) ATCA 8000 AU 260 AU 260 AU 1500 AU 260 AU 260 AU 260 AU ALMA (high-resolution) C22 C38 C39 C42 C35 C40   0  dense core +  Class II CH3OH b a c d e f g no. 1 no. 15 no. 17 no. 3 no. 2 no. 7 no. 30 no. 1 no. 17 no. 2 no. 3 no. 15 no. 30 no. 7 –50°15’06’’ –50°15’04’’ 7 08’’ 0.014 0.012 Continuum flux density (Jy per beam) Continuum flux density (mJy per beam) 1 2 3 4 5 6 7 0.010 0.008 0.006 0.004 0.002 09’’ 12’’ 15’’ 18’’ 52 s 16 h 19 m 51 s no. 21 C26 C12 C6 C17 C10 C29 C13 C15 C11 C16 C5 C4 C1 C3 C8 C14 C9 no. 27 no. 28 no. 23 no. 22 no. 16 no. 19 no. 25 no. 18 no. 6 no. 4 no. 13 no. 12 no. 11 no. 9 no. 8 no. 14 no. 20 no. 29 no. 5 Fig. 1 | Continuum images of ATCA (3.3 mm), ALMA low-resolution (1.3 mm)  and ALMA high-resolution (1.3 mm) observations. a, ATCA 3.3 mm continuum  image (θ ≈ 2.42″). The contour levels are [5, 8, 11, 14, 17, 20, 23, 26, 29] × σ, where  root mean squared (rms) noise of continuum image is σ = 0.6 mJy per beam.   b, ALMA low-resolution (θ ≈ 0.32″) 1.3 mm continuum image. The contour is the  7σ, where σ = 0.16 mJy per beam. The ellipses show the identified cores based  on the low-resolution continuum image. The red pluses are the Class II CH3OH  maser42. c–g, ALMA high-resolution (θ ≈ 0.05″) 1.3 mm continuum image for  multiple systems. The green crosses present the identified condensations based  on the ALMA high-resolution continuum image. The contour is the 7σ, where  σ = 0.05 mJy per beam. The dense cores (no. 1, no. 2, no. 3, …) and condensations  (C1, C2, C3, …) are numbered in order of descending integrated intensity.   c, Dense core no. 2 fragments into quadruple condensation system (C8, C10, C14,  C17) and dense core no. 3 fragments into triple condensation system (C6, C12,  C26). d, Dense core no. 1 fragments into quintuple condensation system (C1, C3,  C4, C5, C16) and dense core no. 7 fragments into binary condensation system  (C11, C29). e, Dense core no. 17 fragments into binary condensation (C22, C38).  f, Dense core no. 30 fragments into binary condensation (C39, C42). g, Dense  core no. 15 fragments into binary condensation (C35, C40). The white ellipses in  the lower left corner of each panel denote the synthesized beam of continuum  images. ICRS, International Celestial Reference System. Nature Astronomy Article https://doi.org/10.1038/s41550-023-02181-9 Extended Data Fig. 6 | Intensity-weighted velocity maps derived from the  high-resolution data toward multiple systems. a–c, Intensity-weighted  velocity maps of CH3CN 124 − 114 (a), 13CH3CN 133 - 123 (b), and CH3OCHO  200,20 − 190,19 (c) for the quadruple system. d-e, Intensity-weighted velocity maps  of CH3OH 42,2 − 31,2 (d) and SO 5, 6 − 4, 5 (e) for the triple and the binary systems,  respectively. The black and magenta ellipses show the condensations and their  parent cores, respectively. The red plusses marks the Class II CH3OH maser  positions. The grey contours show the velocity-integrated intensity maps with  levels of [5, 10, 15, 20, 30] × σrms, where the σrms is 9 mJy beam−1 km s−1 for a–c and 6  mJy beam−1 km s−1 for d–e. The black ellipses in the lower left corner of each panel  denote the synthesized beam of lines images. Nature Astronomy Article https://doi.org/10.1038/s41550-023-02181-9 Extended Data Fig. 7 | Intensity-weighted velocity maps of CH3CN 124 − 114  for two velocity ranges of [-98, -91] km s−1 and [-90, -84] km s−1. The black and  magenta ellipses show the condensations and their parent cores, respectively.  The red plusses marks the Class II CH3OH maser positions. The grey contours  show the velocity-integrated intensity maps with levels of [5, 10, 15, 20, 30] × σrms,  where the σrms is 6 mJy beam−1 km s−1. The black ellipses in the lower left corner of  each panel denote the synthesized beam of lines images. Nature Astronomy Article https://doi.org/10.1038/s41550-023-02181-9 Extended Data Fig. 8 | Molecular outflows seen in SiO emission in the  ALMA low-resolution data. SiO redshifted and blueshifted contours overlaid  on the ALMA low-resolution 1.3 mm continuum. The green and magenta  arrows present the blueshifted and redshifted directions of the SiO outflow.  The cyan ellipses show the dense cores. In panel a, the SiO emission shows a  prominent blueshifted, a clear redshifted, and a weak redshifted component  from dense core #1. In panel b, the SiO emission reveals complicated outflow  spatial morphologies toward dense cores #2 and #3. Dense core #3 drives two  blueshifted outflows. Dense core #2 drives at least two blueshifted and two  redshifted outflows. Contours levels start at 3 σrms and increase in step of 1.5 σrms  interval, where σrms is 0.023 Jy beam−1 km s−1. The synthesized beam size of 1.3  mm continuum image present in the lower left corner. The detected misaligned  outflows further suggest that the quintuple, quadruple, and triple systems are  formed from core fragmentation54.
Title: Observations of high-order multiplicity in a high-mass stellar protocluster ​
Authors: Shanghuo Li, Patricio Sanhueza, Henrik Beuther, Huei-Ru Vivien Chen, Rolf Kuiper, Fernando A. Olguin, Ralph E. Pudritz, Ian W. Stephens, Qizhou Zhang, Fumitaka Nakamura, Xing Lu, Rajika L. Kuruwita, Takeshi Sakai, Thomas Henning, Kotomi Taniguchi, Fei Li ​
Publisher: Nature Astronomy
Date: 2024-01-15 00:00:00
Abstract: The dominant mechanism forming multiple stellar systems in the high-mass regime (M* ≳ 8 M⊙) remained unknown because direct imaging of multiple protostellar systems at early phases of high-mass star formation is very challenging. ​ High-mass stars are expected to form in clustered environments containing binaries and higher-order multiplicity systems. ​ So far only a few high-mass protobinary systems, and no definitive higher-order multiples, have been detected. ​ Here we report the discovery of one quintuple, one quadruple, one triple and four binary protostellar systems simultaneously forming in a single high-mass protocluster, G333.23–0.06, using Atacama Large Millimeter/submillimeter Array high-resolution observations. ​ We present a new example of a group of gravitationally bound binary and higher-order multiples during their early formation phases in a protocluster. ​ This provides the clearest direct measurement of the initial configuration of primordial high-order multiple systems, with implications for the in situ multiplicity and its origin. ​ We find that the binary and higher-order multiple systems, and their parent cores, show no obvious sign of disk-like kinematic structure. ​ We conclude that the observed fragmentation into binary and higher-order multiple systems can be explained by core fragmentation, indicating its crucial role in establishing the multiplicity during high-mass star cluster formation.  