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Asymmetric Line Profiles in Dense Molecular Clumps Observed in MALT90: Evidence for Global Collapse

Jackson, JM, Whitaker, JS, Rathborne, JM, Foster, JB, Contreras, Y, Sanhueza, P, Stephens, IW, Longmore, SN and Allingham, D (2018) Asymmetric Line Profiles in Dense Molecular Clumps Observed in MALT90: Evidence for Global Collapse. Astrophysical Journal, 870 (1). ISSN 0004-637X

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Open Access URL: https://dx.doi.org/10.3847/1538-4357/aaef84 (Published version)

Abstract

Using molecular line data from the Millimetre Astronomy Legacy Team 90 GHz Survey (MALT90), we have searched the optically thick \hcop\, line for the "blue asymmetry" spectroscopic signature of infall motion in a large sample of high-mass, dense molecular clumps observed to be at different evolutionary stages of star cluster formation according to their mid-infrared appearance. To quantify the degree of the line asymmetry, we measure the asymmetry parameter $A = {{I_{blue}-I_{red}}\over{I_{blue}+I_{red}}}$, the fraction of the integrated intensity that lies to the blueshifted side of the systemic velocity determined from the optically thin tracer \nthp. For a sample of 1,093 sources, both the mean and median of $A$ are positive ($A = 0.083\pm0.010$ and $0.065\pm0.009$, respectively) with high statistical significance, and a majority of sources (a fraction of $0.607 \pm 0.015$ of the sample) show positive values of A, indicating a preponderance of blue-asymmetric profiles over red-asymmetric profiles. Two other measures, the local slope of the line at the systemic velocity and the $\delta v$ parameter of \citet{Mardones1997}, also show an overall blue asymmetry for the sample, but with smaller statistical significance. This blue asymmetry indicates that these high-mass clumps are predominantly undergoing gravitational collapse. The blue asymmetry is larger ($A \sim 0.12$) for the earliest evolutionary stages (quiescent, protostellar and compact H II region) than for the later H II region ($A \sim 0.06$) and PDR ($A \sim 0$) classifications.

Item Type: Article
Uncontrolled Keywords: astro-ph.GA; astro-ph.GA
Subjects: Q Science > QB Astronomy
Q Science > QC Physics
Divisions: Astrophysics Research Institute
Publisher: American Astronomical Society; IOP Publishing
Related URLs:
Date Deposited: 05 Feb 2019 12:10
Last Modified: 05 Feb 2019 12:10
URI: http://researchonline.ljmu.ac.uk/id/eprint/9720

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