Kavli Affiliate: Ke Wang
| First 5 Authors: Fengwei Xu, Ke Wang, Tie Liu, Lei Zhu, Guido Garay
| Summary:
Leveraging the high resolution, high sensitivity, and wide frequency coverage
of the Atacama Large Millimeter/submillimeter Array (ALMA), the QUARKS survey,
standing for "Querying Underlying mechanisms of massive star formation with
ALMA-Resolved gas Kinematics and Structures", is observing 139 massive
star-forming clumps at ALMA Band 6 ($lambdasim$ 1.3 mm). This paper
introduces the Atacama Compact Array (ACA) 7-m data. Combining multi-wavelength
data, we provide the first edition of QUARKS atlas, offering insights into the
multiscale and multiphase interstellar medium in high-mass star formation. The
ACA 1.3 mm catalog includes 207 continuum sources that are called ACA sources.
Their gas kinetic temperatures are estimated using three formaldehyde (H$_2$CO)
transitions with a non-LTE radiation transfer model, and the mass and density
are derived from a dust emission model. The ACA sources are massive (16-84
percentile values of 6-160 $M_{odot}$), gravity-dominated ($Mpropto R^{1.1}$)
fragments within massive clumps, with supersonic turbulence ($mathcal{M}>1$)
and embedded star-forming protoclusters. We find a linear correlation between
the masses of the fragments and the massive clumps, with a ratio of 6% between
the two. When considering the fragments as representative of dense gas, the
ratio indicates a dense gas fraction (DGF) of 6%, although with a wide scatter
ranging from 1% to 10%. If we consider the QUARKS massive clumps to be what is
observed at various scales, then the size-independent DGF indicates a
self-similar fragmentation or collapsing mode in protocluster formation. With
the ACA data over four orders of magnitude of luminosity-to-mass ratio ($L/M$),
we find that the DGF increases significantly with $L/M$, which indicates clump
evolutionary stage. We observed a limited fragmentation at the subclump scale,
which can be explained by dynamic global collapse process.
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