Universität zu Köln

Ortiz, Jorge L. Morales, Ceccarelli, Cecilia ORCID: 0000-0001-9664-6292, Lis, Dariusz C., Olmi, Luca ORCID: 0000-0002-1162-7947, Plume, Rene ORCID: 0000-0002-6482-8945 and Schilke, Peter ORCID: 0000-0003-2141-5689 (2014). Ionization toward the high-mass star-forming region NGC 6334 I. Astron. Astrophys., 563. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. Ionization plays a central role in the gas-phase chemistry of molecular clouds. Since ions are coupled with magnetic fields, which can in turn counteract gravitational collapse, it is of paramount importance to measure their abundance in star-forming regions. Aims. We use spectral line observations of the high-mass star-forming region NGC 6334 I to derive the abundance of two of the most abundant molecular ions, HCO+ and N2H+, and consequently, the cosmic ray ionization rate. In addition, the line profiles provide information about the kinematics of this region. Methods. We present high-resolution spectral line observations conducted with the HIFI instrument on board the Herschel Space Observatory of the rotational transitions with J(up) >= 5 of the molecular species (CO)-O-17, (CO)-O-18, HCO+, (HCO+)-C-13, and N2H+. Results. The HCO+ and N2H+ line profiles display a redshifted asymmetry consistent with a region of expanding gas. We identify two emission components in the spectra, each with a different excitation, associated with the envelope of NGC 6334 I. The physical parameters obtained for the envelope are in agreement with previous models of the radial structure of NGC 6334 I based on sub-millimeter continuum observations. Based on our new Herschel/HIFI observations, combined with the predictions from a chemical model, we derive a cosmic ray ionization rate that is an order of magnitude higher than the canonical value of 10(-17) s(-1). Conclusions. We find evidence of an expansion of the envelope surrounding the hot core of NGC 6334 I, which is mainly driven by thermal pressure from the hot ionized gas in the region. The ionization rate seems to be dominated by cosmic rays originating from outside the source, although X-ray emission from the NGC 6334 I core could contribute to the ionization in the inner part of the envelope.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Ortiz, Jorge L. Morales UNSPECIFIED UNSPECIFIED UNSPECIFIED Ceccarelli, Cecilia UNSPECIFIED orcid.org/0000-0001-9664-6292 UNSPECIFIED Lis, Dariusz C. UNSPECIFIED UNSPECIFIED UNSPECIFIED Olmi, Luca UNSPECIFIED orcid.org/0000-0002-1162-7947 UNSPECIFIED Plume, Rene UNSPECIFIED orcid.org/0000-0002-6482-8945 UNSPECIFIED Schilke, Peter UNSPECIFIED orcid.org/0000-0003-2141-5689 UNSPECIFIED
URN:	urn:nbn:de:hbz:38-444093
DOI:	10.1051/0004-6361/201322071
Journal or Publication Title:	Astron. Astrophys.
Volume:	563
Date:	2014
Publisher:	EDP SCIENCES S A
Place of Publication:	LES ULIS CEDEX A
ISSN:	1432-0746
Language:	English
Faculty:	Faculty of Mathematics and Natural Sciences
Divisions:	Faculty of Mathematics and Natural Sciences > Department of Physics > Institute of Physics I
Subjects:	no entry
Uncontrolled Keywords:	Keywords Language COSMIC-RAY IONIZATION; MOLECULAR CLOUD; DENSE CORES; EMISSION; HERSCHEL/HIFI; ULTRACOMPACT; CHEMISTRY; EVOLUTION; CONTINUUM; NGC-6334 Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/44409