Browsing by Subject "CLUMPS"
Now showing items 1-3 of 3
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(2020)We report studies of the relationships between the total bolometric luminosity (L-bol or L-TIR) and the molecular line luminosities of J = 1 - 0 transitions of (HCN)-C-13, (HCO+)-C-13, HCN, and HCO+ with data obtained from ACA observations in the 'ATOMS' survey of 146 active Galactic star-forming regions. The correlations between L-bol and molecular line luminosities L-mol' of the four transitions all appear to be approximately linear. Line emission of isotopologues shows as large scatters in L-bol-L-mol' relations as their main line emission. The log(L-bol/L-mol') for different molecular line tracers have similar distributions. The L-bol-to-L-mol' ratios do not change with galactocentric distances (R-GC) and clump masses (M-clump). The molecular line luminosity ratios (HCN-to-HCO+, (HCN)-C-13-to-(HCO+)-C-13, HCN-to-(HCN)-C-13, and HCO+-to-(HCO+)-C-13) all appear constant against L-bol, dust temperature (T-d), M-clump, and R-GC. Our studies suggest that both the main lines and isotopologue lines are good tracers of the total masses of dense gas in Galactic molecular clumps. The large optical depths of main lines do not affect the interpretation of the slopes in star formation relations. We find that the mean star formation efficiency (SFE) of massive Galactic clumps in the 'ATOMS' survey is reasonably consistent with other measures of the SFE for dense gas, even those using very different tracers or examining very different spatial scales.
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(2022)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 (HCO+)-C-13 (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 similar to 0.04 pc and 0.2 km s(-1), respectively. Several tens of dendrogram structures have been extracted in the position-position-velocity space of (HCO+)-C-13, which include 21 small-scale leaves and 20 larger-scale branches. Overall, their gas motions are supersonic but they exhibit the interesting behaviour 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.
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(2022)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+/(HCO+)-C-13 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 similar to 45 M-circle dot, and a total energy of 1 x 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.
