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Complex Organic Molecules In Accretion Shocks Around A Hot Core Precursor
Zeroth moment maps of some simple molecules, and selected transitions of COMs.
All contours correspond to significant emission and start at 20% of the maximum value and increase by 15% of the maximum value. Yellow star marks the position of the dust continuum peak corresponding to the central protostar. The beam is shown in the lower left corner. Labels indicate the shown molecular species. One figure shows the continuum as a reference, where the scale and contours are the same as in Fig. 1.
Classical hot cores are rich in molecular emission, and they show a high abundance of complex organic molecules (COMs). The emergence of molecular complexity is poorly constrained in the early evolution of hot cores.
Using the Atacama Large Millimeter Array we put observational constraints on the physical location of COMs in a high-mass protostellar envelope associated with the G328.2551-0.5321 clump. The protostar is single down to ~400au scales and we resolve the emission region of COMs. Using thermodynamic equilibrium modelling of the available 7.5 GHz bandwidth around ~345 GHz, we detect emission from 10 COMs, and identify a line of deuterated water (HDO).
The most extended emission originates from methanol, methyl formate and formamide. Together with HDO, these molecules are found to be associated with both the accretion shocks and the inner envelope, for which we estimate a moderate temperature of Tkin∼110 K. Our findings reveal a significant difference in the distribution of COMs. O-bearing COMs, such as ethanol, acetone, and ethylene glycol are almost exclusively found and show a higher abundance towards the accretion shocks with Tkin∼180 K. Whereas N-bearing COMs with a CN group, such as vinyl and ethyl cyanide peak on the central position, thus the protostar and the accretion disk.
This is the first observational evidence for a large column density of COMs seen towards accretion shocks at the centrifugal barrier at the inner envelope. Since the molecular composition is dominated by that of the accretion shocks and the radiatively heated hot inner region is very compact, we propose this source to be a precursor to a classical, radiatively heated hot core.
T. Csengeri, A. Belloche, S. Bontemps, F. Wyrowski, K. M. Menten, L. Bouscasse
(Submitted on 13 Oct 2019)
Comments: Accepted for publication in A&A (17 pages, 9 figures). The abstract is abbreviated
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:1910.05830 [astro-ph.GA] (or arXiv:1910.05830v1 [astro-ph.GA] for this version)
From: Timea Csengeri Dr.
[v1] Sun, 13 Oct 2019 21:05:11 UTC (3,487 KB)