Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Hong-Li Liu
Tie Liu
Neal J. Evans
Ke Wang
Guido Garay
Sheng-Li Qin
Shanghuo Li
Amelia Stutz
Paul F. Goldsmith
Sheng-Yuan Liu
Anandmayee Tej
Qizhou Zhang
Mika Juvela
Di Li
Jun-Zhi Wang
Leonardo Bronfman
Zhiyuan Ren
Yue-Fang Wu
Kee-Tae Kim
Chang-Won Lee
Abstract： We have identified 453 compact dense cores in 3 mm continuum emission maps in the ATOMS (ALMA Three-millimeter Observations of Massive Star-forming regions) survey, and compiled three catalogues of high-mass star forming cores. One catalogue, referred to as H/UC-HII catalogue, includes 89 cores that enshroud hyper/ultra compact (H/UC) HII regions as characterized by associated compact H40alpha emission. A second catalogue, referred to as pure s-cHMC, includes 32 candidate Hot Molecular Cores (HMCs) showing rich spectra (N>20lines) of complex organic molecules (COMs) but not associated with H/UC-HII regions. The third catalogue, referred to as pure w-cHMC, includes 58 candidate HMCs with relatively low levels of COM richness and not associated with H/UC-HII regions. These three catalogues of dense cores provide an important foundation for future studies of the early stages of high-mass star formation across the Milky Way. We also find that nearly half of H/UC-HII cores are candidate HMCs. From the number counts of COM-containing and H/UC-HII cores, we suggest that the duration of high-mass protostellar cores showing chemically rich features is at least comparable to the lifetime of H/UC-HII regions. For cores in the H/UC-HII catalogue, the width of the H40alpha line increases as the core size decreases, suggesting that the non-thermal dynamical and/or pressure line-broadening mechanisms dominate on the smaller scales of the H/UC-HII cores.
Peer Review Status:
Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Shih-Ying Hsu
Sheng-Yuan Liu
Tie Liu
Dipen Sahu
Chin-Fei Lee
Kenichi Tatematsu
Kee-Tae Kim
Naomi Hirano
Yao-Lun Yang
Doug Johnstone
Hongli Liu
Mika Juvela
Leonardo Bronfman
Huei-Ru Vivien Chen
Somnath Dutta
David J. Eden
Kai-Syun Jhan
Yi-Jehng Kuan
Chang Won Lee
Jeong-Eun Lee
Abstract： The presence of complex organic molecules (COMs) in the interstellar medium (ISM) is of great interest since it may link to the origin and prevalence of life in the universe. Aiming to investigate the occurrence of COMs and their possible origins, we conducted a chemical census toward a sample of protostellar cores as part of the ALMA Survey of Orion Planck Galactic Cold Clumps (ALMASOP) project. We report the detection of 11 hot corino sources, which exhibit compact emissions from warm and abundant COMs, among 56 Class 0/I protostellar cores. All the hot corino sources discovered are likely Class 0 and their sizes of the warm region ($>$ 100 K) are comparable to 100 au. The luminosity of the hot corino sources exhibits positive correlations with the total number of methanol and the extent of its emissions. Such correlations are consistent with the thermal desorption picture for the presence of hot corino and suggest that the lower luminosity (Class 0) sources likely have a smaller region with COMs emissions. With the same sample selection method and detection criteria being applied, the detection rates of the warm methanol in the Orion cloud (15/37) and the Perseus cloud (28/50) are statistically similar when the cloud distances and the limited sample size are considered. Observing the same set of COM transitions will bring a more informative comparison between the cloud properties.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 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
Abstract： 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$1~pc dramatically increase as filament lengths decrease, indicating that the gravity of the hubs or cores starts to dominate gas infall at small scales. We suggest that self-similar hub-filament systems and filamentary accretion at all scales may play a key role in high-mass star formation.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Qiuyi Luo
Tie Liu
Kenichi Tatematsu
ShengYuan Liu
Pak Shing Li
James di Francesco
Doug Johnstone
Paul F. Goldsmith
Somnath Dutta
Naomi Hirano
ChinFei Lee
Di Li
KeeTae Kim
Chang Won Lee
JeongEun Lee
Xunchuan Liu
Mika Juvela
Jinhua He
ShengLi Qin
HongLi Liu
Abstract： During the transition phase from a prestellar to a protostellar cloud core, one or several protostars can form within a single gas core. The detailed physical processes of this transition, however, still remain unclear. We present 1.3 mm dust continuum and molecular line observations with the Atacama Large Millimeter/submillimeter Array (ALMA) toward 43 protostellar cores in the Orion Molecular Cloud Complex ($\lambda$ Orionis, Orion B, and Orion A) with an angular resolution of $\sim$ 0.35" ($\sim$ 140 au). In total, we detect 13 binary/multiple systems. We derive an overall multiplicity frequency (MF) of 28$\%$ $\pm$ 4$\%$ and a companion star fraction (CSF) of 51$\%$ $\pm$ 6$\%$, over a separation range of 300-8900 au. The median separation of companions is about 2100 au. The occurrence of stellar multiplicity may depend on the physical characteristics of the dense cores. Notably, those containing binary/multiple systems tend to show higher gas density and Mach number than cores forming single stars. The integral-shaped filament (ISF) of Orion A giant molecular cloud (GMC), which has the highest gas density and hosts high-mass star formation in its central region (the Orion Nebula cluster), shows the highest MF and CSF among the Orion GMCs. In contrast, the $\lambda$ Orionis Giant Molecular Cloud (GMC) has a lower MF and CSF than the Orion B and Orion A GMCs, indicating that feedback from HII regions may suppress the formation of multiple systems. We also find that the protostars comprising a binary/multiple system are usually at different evolutionary stages.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Dipen Sahu
Sheng-Yuan Liu
Doug Johnstone
Tie Liu
Neal J. Evans
Naomi Hirano
Kenichi Tatematsu
James Di Francesco
Chin-Fei Lee
Kee-Tae Kim
Somnath Dutta
Shih-Ying Hsu
Shanghuo Li
Qiu-Yi Luo
Patricio Sanhueza
Hsien Shang
Alessio Traficante
Mika Juvela
Chang Won Lee
David J. Eden
Abstract： Starless cores represent the initial stage of evolution toward (proto)star formation, and a subset of them, known as prestellar cores, with high density (~ 10^6 cm^-3 or higher) and being centrally concentrated are expected to be embryos of (proto)stars. Determining the density profile of prestellar cores, therefore provides an important opportunity to gauge the initial conditions of star formation. In this work, we perform rigorous modeling to estimate the density profiles of three nearly spherical prestellar cores among a sample of five highly dense cores detected by our recent observations. We employed multi-scale observational data of the (sub)millimeter dust continuum emission including those obtained by SCUBA-2 on the JCMT with a resolution of ~5600 au and by multiple ALMA observations with a resolution as high as ~480 au. We are able to consistently reproduce the observed multi-scale dust continuum images of the cores with a simple prescribed density profile, which bears an inner region of flat density and a r^-2 profile toward the outer region. By utilizing the peak density and the size of the inner flat region as a proxy for the dynamical stage of the cores, we find that the three modeled cores are most likely unstable and prone to collapse. The sizes of the inner flat regions, as compact as ~500 au, signify them being the highly evolved prestellar cores rarely found to date.
Peer Review Status:Awaiting Review
Subjects: Astronomy >> Astrophysical processes submitted time 2023-02-19
Jian-Wen Zhou
Tie Liu
Jin-Zeng Li
Hong-Li Liu
Ke Wang
Feng-Wei Xu
Kee-Tae Kim
Chang Won Lee
Lokesh Dewangan
Kenichi Tatematsu
Shanghuo Li
Xun-Chuan Liu
Mengyao Tang
Zhiyuan Ren
Guo-Yin Zhang
Chao Zhang
Rong Liu
Qiu-Yi Luo
Isabelle Ristorcelli
Abstract： Filaments play an important role in star formation, but the formation process of filaments themselves is still unclear. The high-mass star forming clump G286.21+0.17 (G286 for short) that contains an "L" type filament was thought to undergo global collapse. Our high resolution ALMA band 3 observations resolve the gas kinematics of G286 and reveal two sub-clumps with very different velocities inside it. We find that the "blue profile" (an indicator of gas infall) of HCO+ lines in single dish observations of G286 is actually caused by gas emission from the two sub-clumps rather than gas infall. We advise great caution in interpreting gas kinematics (e.g., infall) from line profiles toward distant massive clumps in single dish observations. Energetic outflows are identified in G286 but the outflows are not strong enough to drive expansion of the two sub-clumps. The two parts of the "L" type filament ("NW-SE" and "NE-SW" filaments) show prominent velocity gradients perpendicular to their major axes, indicating that they are likely formed due to large-scale compression flows. We argue that the large-scale compression flows could be induced by the expansion of nearby giant HII regions. The "NW-SE" and "NE-SW" filaments seem to be in collision, and a large amount of gas has been accumulated in the junction region where the most massive core G286c1 forms.
Peer Review Status:Awaiting Review
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