分类： 天文学 >> 天文学 提交时间： 2023-02-19
Jian-Wen Zhou
Tie Liu
Neal J. Evans
Guido Garay
Paul F. Goldsmith
Gilberto C. Gomez
Enrique Vazquez-Semadeni
Hong-Li Liu
Amelia M. Stutz
Ke Wang
Mika Juvela
Jinhua He
Di Li
Leonardo Bronfman
Xunchuan Liu
Feng-Wei Xu
Anandmayee Tej
L. K. Dewangan
Shanghuo Li
Siju Zhang
摘要： We investigate the presence of hub-filament systems in a large sample of 146 active proto-clusters, using H$^{13}$CO$^{+}$ J=1-0 molecular line data obtained from the ATOMS survey. We find that filaments are ubiquitous in proto-clusters, and hub-filament systems are very common from dense core scales ($\sim$0.1 pc) to clump/cloud scales ($\sim$1-10 pc). The proportion of proto-clusters containing hub-filament systems decreases with increasing dust temperature ($T_d$) and luminosity-to-mass ratios ($L/M$) of clumps, indicating that stellar feedback from H{\sc ii} regions gradually destroys the hub-filament systems as proto-clusters evolve. Clear velocity gradients are seen along the longest filaments with a mean velocity gradient of 8.71 km s$^{-1}$pc$^{-1}$ and a median velocity gradient of 5.54 km s$^{-1}$pc$^{-1}$. We find that velocity gradients are small for filament lengths larger than $\sim$1~pc, probably hinting at the existence of inertial inflows, although we cannot determine whether the latter are driven by large-scale turbulence or large-scale gravitational contraction. In contrast, velocity gradients below $\sim$1~pc dramatically increase as filament lengths decrease, indicating that the gravity of the hubs or cores starts to dominate gas infall at small scales. We suggest that self-similar hub-filament systems and filamentary accretion at all scales may play a key role in high-mass star formation.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hong-Li Liu
Anandmayee Tej
Tie Liu
Paul F. Goldsmith
Amelia Stutz
Mika Juvela
Sheng-Li Qin
Feng-Wei Xu
Leonardo Bronfman
Neal J. Evans
Anindya Saha
Namitha Issac
Ken'ichi Tatematsu
Ke Wang
Shanghuo Li
Siju Zhang
Tapas Baug
Lokesh Dewangan
Yue-Fang Wu
Yong Zhang
摘要： We present a comprehensive study of the gas kinematics associated with density structures at different spatial scales in the filamentary infrared dark cloud, G034.43+00.24 (G34). This study makes use of the H13CO+ (1-0) molecular line data from the ALMA Three-millimeter Observations of Massive Star-forming regions (ATOMS) survey, which has spatial and velocity resolution of 0.04 pc and 0.2 km/s, respectively. Several tens of dendrogram structures have been extracted in the position-position-velocity space of H13CO+, which include 21 small-scale leaves and 20 larger-scale branches. Overall, their gas motions are supersonic but they exhibit the interesting behavior where leaves tend to be less dynamically supersonic than the branches. For the larger-scale, branch structures, the observed velocity-size relation (i.e., velocity variation/dispersion versus size) are seen to follow the Larson scaling exponent while the smaller-scale, leaf structures show a systematic deviation and display a steeper slope. We argue that the origin of the observed kinematics of the branch structures is likely to be a combination of turbulence and gravity-driven ordered gas flows. In comparison, gravity-driven chaotic gas motion is likely at the level of small-scale leaf structures. The results presented in our previous paper and this current follow-up study suggest that the main driving mechanism for mass accretion/inflow observed in G34 varies at different spatial scales. We therefore conclude that a scale-dependent combined effect of turbulence and gravity is essential to explain the star-formation processes in G34.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hong-Li Liu
Anandmayee Tej
Tie Liu
Patricio Sanhueza
Shengli Qin
Jinhua He
Paul F. Goldsmith
Guido Garay
Sirong Pan
Kaho Morii
Shanghuo Li
Amelia Stutz
Keníchi Tatematsu
Feng-Wei Xu
Leonardo Bronfman
Anindya Saha
Namitha Issac
Tapas Baug
L. Viktor Toth
Lokesh Dewangan
摘要： We present a statistical study of a sample of 17 hub-filament-system (HFS) clouds of high-mass star formation using high-angular resolution ($\sim$1-2 arcsecond) ALMA 1.3mm and 3mm continuum data. The sample includes 8 infrared (IR)-dark and 9 IR-bright types, which correspond to an evolutionary sequence from the IR-dark to IR-bright stage. The central massive clumps and their associated most massive cores are observed to follow a trend of increasing mass ($M$) and mass surface density ($\Sigma$) with evolution from IR-dark to IR-bright stage. In addition, a mass-segregated cluster of young stellar objects (YSOs) are revealed in both IR-dark and IR-bright HFSs with massive YSOs located in the hub and the population of low-mass YSOs distributed over larger areas. Moreover, outflow feedback in all HFSs are found to escape preferentially through the inter-filamentary diffuse cavities, suggesting that outflows would render a limited effect on the disruption of the HFSs and ongoing high-mass star formation therein. From the above observations, we suggest that high-mass star formation in the HFSs can be described by a multi-scale mass accretion/transfer scenario, from hub-composing filaments through clumps down to cores, that can naturally lead to a mass-segregated cluster of stars.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hong-Li Liu
Anandmayee Tej
Tie Liu
Patricio Sanhueza
Shengli Qin
Jinhua He
Paul F. Goldsmith
Guido Garay
Sirong Pan
Kaho Morii
Shanghuo Li
Amelia Stutz
Keníchi Tatematsu
Feng-Wei Xu
Leonardo Bronfman
Anindya Saha
Namitha Issac
Tapas Baug
L. Viktor Toth
Lokesh Dewangan
摘要： We present a statistical study of a sample of 17 hub-filament-system (HFS) clouds of high-mass star formation using high-angular resolution ($\sim$1-2 arcsecond) ALMA 1.3mm and 3mm continuum data. The sample includes 8 infrared (IR)-dark and 9 IR-bright types, which correspond to an evolutionary sequence from the IR-dark to IR-bright stage. The central massive clumps and their associated most massive cores are observed to follow a trend of increasing mass ($M$) and mass surface density ($\Sigma$) with evolution from IR-dark to IR-bright stage. In addition, a mass-segregated cluster of young stellar objects (YSOs) are revealed in both IR-dark and IR-bright HFSs with massive YSOs located in the hub and the population of low-mass YSOs distributed over larger areas. Moreover, outflow feedback in all HFSs are found to escape preferentially through the inter-filamentary diffuse cavities, suggesting that outflows would render a limited effect on the disruption of the HFSs and ongoing high-mass star formation therein. From the above observations, we suggest that high-mass star formation in the HFSs can be described by a multi-scale mass accretion/transfer scenario, from hub-composing filaments through clumps down to cores, that can naturally lead to a mass-segregated cluster of stars.
分类： 天文学 >> 天文学 提交时间： 2023-02-19
Hong-Li Liu
Anandmayee Tej
Tie Liu
Namitha Issac
Anindya Saha
Paul F. Goldsmith
Jun-Zhi Wang
Qizhou Zhang
Sheng-Li Qin
Ke Wang
Shanghuo Li
Archana Soam
Lokesh Dewangan
Chang Won Lee
Pak-Shing Li
Xun-Chuan Liu
Yong Zhang
Zhiyuan Ren
Mika Juvela
Leonardo Bronfman
摘要： We present new 3-mm continuum and molecular lines observations from the ATOMS survey towards the massive protostellar clump, MM1, located in the filamentary infrared dark cloud (IRDC), G034.43+00.24 (G34). The lines observed are the tracers of either dense gas (e.g. HCO+/H13CO+ J = 1-0) or outflows (e.g. CS J = 2-1). The most complete picture to date of seven cores in MM1 is revealed by dust continuum emission. These cores are found to be gravitationally bound, with virial parameter, $\alpha_{vir}<2$. At least four outflows are identified in MM1 with a total outflowing mass of $\sim 45 M_\odot$, and a total energy of $\sim 1\times 10^{47}$ erg, typical of outflows from a B0-type star. Evidence of hierarchical fragmentation, where turbulence dominates over thermal pressure, is observed at both the cloud and the clump scales. This could be linked to the scale-dependent, dynamical mass inflow/accretion on clump and core scales. We therefore suggest that the G34 cloud could be undergoing a dynamical mass inflow/accretion process linked to the multiscale fragmentation, which leads to the sequential formation of fragments of the initial cloud, clumps, and ultimately dense cores, the sites of star formation.
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