Universität zu Köln

Bonfand, M., Belloche, A., Garrod, R. T., Menten, K. M., Willis, E., Stephan, G. and Mueller, H. S. P. (2019). The complex chemistry of hot cores in Sgr B2(N): influence of cosmic-ray ionization and thermal history. Astron. Astrophys., 628. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. As the number of complex organic molecules (COMs) detected in the interstellar medium increases, it becomes even more important to place meaningful constraints on the origins and formation pathways of such chemical species. The molecular cloud Sagittarius B2(N) is host to several hot molecular cores in the early stage of star formation, where a great variety of COMs are detected in the gas phase. Given its exposure to the extreme conditions of the Galactic center (GC) region, Sgr B2(N) is one of the best targets to study the impact of environmental conditions on the production of COMs. Aims. Our main goal is to characterize the physico-chemical evolution of Sgr B2(N)'s sources in order to explain their chemical differences and constrain their environmental conditions. Methods. The chemical composition of Sgr B2(N)'s hot cores, N2, N3, N4, and N5 is derived by modeling their 3 mm emission spectra extracted from the Exploring Molecular Complexity with ALMA (EMoCA) imaging spectral line survey performed with the Atacama Large Millimeter/submillimeter Array (ALMA). We derived the density distribution in the envelope of the sources based on the masses computed from the ALMA dust continuum emission maps. We used the radiative transfer code RADMC-3D to compute temperature profiles and inferred the current luminosity of the sources based on the COM rotational temperatures derived from population diagrams. We used published results of 3D radiation-magnetohydrodynamical (RMHD) simulations of high-mass star formation to estimate the time evolution of the source properties. We employed the astrochemical code MAGICKAL to compute time-dependent chemical abundances in the sources and to investigate how physical properties and environmental conditions influence the production of COMs. Results. The analysis of the abundances of 11 COMs detected toward Sgr B2(N2-N5) reveals that N3 and N5 share a similar chemical composition while N2 differs significantly from the other sources. We estimate the current luminosities of N2, N3, N4, and N5 to be 2.6 x 10(5) L-circle dot, 4.5 x 10(4) L-circle dot, 3.9 x 10(5) L-circle dot, and 2.8 x 10(5) L-circle dot, respectively. We find that astrochemical models with a cosmic-ray ionization rate of 7 x 10(-16) s(-1) best reproduce the abundances with respect to methanol of ten COMs observed toward Sgr B2(N2-N5). We also show that COMs still form efficiently on dust grains with minimum dust temperatures in the prestellar phase as high as 15 K, but that minimum temperatures higher than 25K are excluded. Conclusions. The chemical evolution of Sgr B2(N2-N5) strongly depends on their physical history. A more realistic description of the hot cores' physical evolution requires a more rigorous treatment with RMHD simulations tailored to each hot core.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Bonfand, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Belloche, A. UNSPECIFIED UNSPECIFIED UNSPECIFIED Garrod, R. T. UNSPECIFIED UNSPECIFIED UNSPECIFIED Menten, K. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Willis, E. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stephan, G. UNSPECIFIED UNSPECIFIED UNSPECIFIED Mueller, H. S. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-134494
DOI:	10.1051/0004-6361/201935523
Journal or Publication Title:	Astron. Astrophys.
Volume:	628
Date:	2019
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Unspecified
Divisions:	Unspecified
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language GALACTIC-CENTER; STAR-FORMATION; CHEMICAL-MODELS; H-I; DUST; CLOUDS; GAS; SUBMILLIMETER; CONTINUUM; EMISSION Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/13449