The ALMA Survey of 70 μm Dark High-mass Clumps in Early Stages (ASHES). I. Pilot Survey: Clump Fragmentation
Artikel i vetenskaplig tidskrift, 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.

Författare

Patricio Sanhueza

National Astronomical Observatory of Japan

Y. Contreras

Universiteit Leiden

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-Gesellschaft

G. Garay

Universidad de 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

Universität zu Köln

Quang Nguyen-Luong

National Astronomical Observatory of Japan

IBM Canada Ltd.

Daniel Tafoya

Chalmers, Rymd-, geo- och miljövetenskap, Onsala rymdobservatorium, Onsala rymdobservatorium, Observationssupport

Astrophysical Journal

0004-637X (ISSN) 1538-4357 (eISSN)

Vol. 886 2 102

Ämneskategorier

Analytisk kemi

Astronomi, astrofysik och kosmologi

Atom- och molekylfysik och optik

Infrastruktur

Onsala rymdobservatorium

DOI

10.3847/1538-4357/ab45e9

Mer information

Senast uppdaterat

2020-01-30