Universität zu Köln

Tiwari, M., Menten, K. M., Wyrowski, F., Perez-Beaupuits, J. P., Wiesemeyer, H., Guesten, R., Klein, B. and Henkel, C. (2018). Unveiling the remarkable photodissociation region of Messier 8. Astron. Astrophys., 615. LES ULIS CEDEX A: EDP SCIENCES S A. ISSN 1432-0746

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Abstract

Aims. Messier 8 (M8) is one of the brightest HII regions in the sky. We collected an extensive dataset comprising multiple sub-millimeter spectral lines from neutral and ionized carbon and from CO. Based on this dataset, we aim to understand the morphology of M8 and that of its associated photodissociation region (PDR) and to carry out a quantitative analysis of the physical conditions of these regions such as kinetic temperatures and volume densities. Methods. We used the Stratospheric Observatory For Infrared Astronomy (SOFIA), the Atacama Pathfinder Experiment (APEX) 12 m, and the Institut de Radioastronomie Millimetrique (IRAM) 30 m telescopes to perform a comprehensive imaging survey of the emission from the fine structure lines of [C II] and [C I] and multiple rotational transitions of carbon monoxide (CO) isotopologs within 1.3 x 1.3 pc around the dominant Herschel 36 (Her 36) system, which is composed of at least three massive stars. To further explore the morphology of the region, we compared archival infrared, optical, and radio images of the nebula with our newly obtained fine structure line and CO data, and in particular with the velocity information these data provide. We performed a quantitative analysis, using both LTE and non-LTE methods to determine the abundances of some of the observed species, kinetic temperatures, and volume densities. Results. Bright CO, [C II] and [C I] emission have been found toward the HII region and the PDR in M8. Our analysis places the bulk of the molecular material in the background of the nebulosity illuminated by the bright stellar systems Her 36 and 9 Sagitarii. Since the emission from all observed atomic and molecular tracers peaks at or close to the position of Her 36, we conclude that the star is still physically close to its natal dense cloud core and heats it. A veil of warm gas moves away from Her 36 toward the Sun and its associated dust contributes to the foreground extinction in the region. One of the most prominent star forming regions in M8, the Hourglass Nebula, is particularly bright due to cracks in this veil close to Her 36. We obtain H-2 densities ranging from similar to 10(4)-10(6) cm(-3) and kinetic temperatures of 100-150 K in the bright PDR caused by Her 36 using radiative transfer modeling of various transitions of CO isotopologs.

Item Type:	Journal Article
Creators:	Creators Email ORCID ORCID Put Code Tiwari, M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Menten, K. M. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wyrowski, F. UNSPECIFIED UNSPECIFIED UNSPECIFIED Perez-Beaupuits, J. P. UNSPECIFIED UNSPECIFIED UNSPECIFIED Wiesemeyer, H. UNSPECIFIED UNSPECIFIED UNSPECIFIED Guesten, R. UNSPECIFIED UNSPECIFIED UNSPECIFIED Klein, B. UNSPECIFIED UNSPECIFIED UNSPECIFIED Henkel, C. UNSPECIFIED UNSPECIFIED UNSPECIFIED
URN:	urn:nbn:de:hbz:38-179326
DOI:	10.1051/0004-6361/201732437
Journal or Publication Title:	Astron. Astrophys.
Volume:	615
Date:	2018
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 H II REGIONS; LAGOON NEBULA; SUBMILLIMETER OBSERVATIONS; INTERSTELLAR-MEDIUM; MOLECULAR-EMISSION; ORION-BAR; MILLIMETER; CLUSTER; HOURGLASS; M8 Multiple languages Astronomy & Astrophysics Multiple languages
Refereed:	Yes
URI:	http://kups.ub.uni-koeln.de/id/eprint/17932