Universität zu Köln

Garcia, P., Abel, N., Roellig, M., Simon, R. and Stutzki, J. (2021). Warm ISM in the Sgr A complex II. The [C/N] abundance ratio traced by [CII] 158 mu m and [NII] 205 mu m observations toward the Arched Filaments at the Galactic center. Astron. Astrophys., 650. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Context. The Arches Cluster - Arched Filaments (AF) system is our Galaxy's prime example of the complexity involved in the interaction between the strong radiation field of numerous OB stars and their surrounding ISM in extremely harsh environments such as the Galactic center (GC) of the Milky Way. It offers a unique opportunity to study the close relationship between photon-dominated regions (PDRs) and H II regions and their relative contributions to the observed [CII] emission. Aims. We aim to investigate the I([CII]) versus I([NII]) integrated intensity behavior in the AF region in order to assess the [CII] emission contribution from the H II region, which is traced by [NII] line observations, and PDR components in the high-metallicity environment of the GC. Methods. We used [CII] 158 mu m and [NII] 205 mu m fine structure line observations of the AF in the literature to compare their observational integrated intensity distribution to semi-theoretical predictions for the contribution of H II regions and adjacent PDRs to the observed [CII] emission. We explored variations in the [C/N] elemental abundance ratio to explain the overall behavior of the observed relationship. Based on our models, the H II region and PDR contributions to the observed [CII] emission is calculated for a few positions within and near to the AF. Estimates for the [C/N] abundance ratio and [N/H] nitrogen elemental abundance in the AF can then be derived. Results. The behavior of the I([CII]) versus I([NII]) relationship in the AF can be explained by model results satisfying 0.84 < [C/N](AF) < 1.41, with model metallicities ranging from 1 Z(circle dot) to 2 Z(circle dot), hydrogen volume density log n(H) = 3.5, and ionization parameters log U from -1 to -2. A least-squares fit to the model data points yields log I([CII]) = 1.068 x log I([NII]) + 0.645 to predict the [CII] emission arising from the H II regions in the AF. The fraction of the total observed [CII] emission arising from within PDRs varies between similar to 0.20 and similar to 0.75. Our results yield average values for the carbon-to-nitrogen ratio and nitrogen elemental abundances of [C/N](AF) = 1.13 +/- 0.09 and [N/H] AF = 6.21 x 10(-4) for the AF, respectively. They are a factor of similar to 0.4 smaller and similar to 7.5 larger than their corresponding Galactic disk values. Conclusions. The large spatial variation of the fraction of [CII] emission arising either from H II regions or PDRs suggests that both contributions must be disentangled before any modeling attempt is made to explain the observed [CII] emission in the AF. We suggest that secondary production of nitrogen from low- to intermediate-mass stars in the Galactic bulge is a plausible mechanism to explain the large abundance differences between the GC and the Galactic disk. The mass loss of such stars would enrich the GC ISM with nitrogen as the gas falls into the inner GC orbits where the AF are located. Overall, our results show that tight constraints are needed on the [C/N] abundance ratio for the GC, significantly tighter than previous abundance measurements have discerned.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Garcia, P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Abel, N. UNSPECIFIED UNSPECIFIED UNSPECIFIED Roellig, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Simon, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Stutzki, J. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-587937
DOI:	10.1051/0004-6361/202039295
Journal or Publication Title:	Astron. Astrophys.
Volume:	650
Date:	2021
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 INTERSTELLAR EXTINCTION LAW; CENTER MOLECULAR CLOUDS; K-S BANDS; C-II; PLANE SURVEY; RADIO ARC; RECOMBINATION LINE; STAR-FORMATION; MASSIVE STARS; M EMISSION Multiple languages Astronomy & Astrophysics Multiple languages
URI:	http://kups.ub.uni-koeln.de/id/eprint/58793