The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). I. Pilot Survey: Clump Fragmentation
Journal article, 2019
© 2019. The American Astronomical Society. All rights reserved. The ALMA Survey of 70 μm dark High-mass clumps in Early Stages (ASHES) is designed to systematically characterize the earliest stages and constrain theories of high-mass star formation. Twelve massive (>500 M⊙ ), cold (≤15 K), 3.6-70 μm dark prestellar clump candidates, embedded in infrared dark clouds, were carefully selected in the pilot survey to be observed with the Atacama Large Millimeter/submillimeter Array (ALMA). We have mosaicked each clump (∼1 arcmin2) in continuum and line emission with the 12 m, 7 m, and Total Power (TP) arrays at 224 GHz (1.34 mm), resulting in ∼1.″2 resolution (∼4800 au, at the average source distance). As the first paper in the series, we concentrate on the continuum emission to reveal clump fragmentation. We detect 294 cores, from which 84 (29%) are categorized as protostellar based on outflow activity or "warm core" line emission. The remaining 210 (71%) are considered prestellar core candidates. The number of detected cores is independent of the mass sensitivity range of the observations and, on average, more massive clumps tend to form more cores. We find a large population of low-mass (<1 M⊙) cores and no high-mass (>30 M⊙) prestellar cores (maximum mass 11 M⊙). From the prestellar core mass function, we derive a power-law index of 1.17 ± 0.10, which is slightly shallower than Salpeter. We used the minimum spanning tree (MST) technique to characterize the separation between cores and their spatial distribution, and to derive mass segregation ratios. While there is a range of core masses and separations detected in the sample, the mean separation and mass per clump are well explained by thermal Jeans fragmentation and are inconsistent with turbulent Jeans fragmentation. Core spatial distribution is well described by hierarchical subclustering rather than centrally peaked clustering. There is no conclusive evidence of mass segregation. We test several theoretical conditions and conclude that overall, competitive accretion and global hierarchical collapse scenarios are favored over the turbulent core accretion scenario.
Author
Patricio Sanhueza
National Astronomical Observatory of Japan
Y. Contreras
Leiden University
Benjamin Wu
National Astronomical Observatory of Japan
J. M. Jackson
NASA Ames Research Center
Andrés E. Guzmán
National Astronomical Observatory of Japan
Q. Zhang
Harvard-Smithsonian Center for Astrophysics
Shanghuo Li
Harvard-Smithsonian Center for Astrophysics
Chinese Academy of Sciences
Shanghai Astronomical Observatory
X. Lu
National Astronomical Observatory of Japan
A. Silva
National Astronomical Observatory of Japan
Natsuko Izumi
National Astronomical Observatory of Japan
Ibaraki University
Tie Liu
Shanghai Astronomical Observatory
R.E. Miura
National Astronomical Observatory of Japan
Ken'ichi Tatematsu
National Astronomical Observatory of Japan
T. Sakai
University of Electro-Communications
H. Beuther
Max Planck Society
G. Garay
University of Chile (UCH)
Satoshi Ohashi
RIKEN
National Astronomical Observatory of Japan
Masao Saito
National Astronomical Observatory of Japan
Fumitaka Nakamura
National Astronomical Observatory of Japan
Kazuya Saigo
National Astronomical Observatory of Japan
V. S. Veena
University of Cologne
Quang Nguyen-Luong
National Astronomical Observatory of Japan
IBM Canada Ltd.
Daniel Tafoya
Chalmers, Space, Earth and Environment, Onsala Space Observatory
Astrophysical Journal
0004-637X (ISSN) 1538-4357 (eISSN)
Vol. 886 2 102Subject Categories
Analytical Chemistry
Astronomy, Astrophysics and Cosmology
Atom and Molecular Physics and Optics
Infrastructure
Onsala Space Observatory
DOI
10.3847/1538-4357/ab45e9