[C II] 158 μm line emission from Orion A. II. Photodissociation region physics

Autor(en)

C. H. M. Pabst, J. R. Goicoechea, A. Hacar, D. Teyssier, O. Berné, M. G. Wolfire, R. D. Higgins, E. T. Chambers, S. Kabanovic, R. Güsten, J. Stutzki, C. Kramer, A. G. G. M. Tielens

Abstrakt

Context. The [C II] 158 μm fine-structure line is the dominant

cooling line of moderate-density photodissociation regions (PDRs)

illuminated by moderately bright far-ultraviolet (FUV) radiation fields.

This makes this line a prime diagnostic for extended regions illuminated

by massive stars. Aims: We aim to understand the origin of [C II]

emission and its relation to other tracers of gas and dust in PDRs. One

focus is a study of the heating efficiency of interstellar gas as traced

by the [C II] line to test models of the photoelectric heating of

neutral gas by polycyclic aromatic hydrocarbon (PAH) molecules and very

small grains. Methods: We make use of a one-square-degree map of

velocity-resolved [C II] line emission toward the Orion Nebula complex,

and split this out into the individual spatial components, the expanding

Veil Shell, the surface of OMC4, and the PDRs associated with the

compact H II region of M43 and the reflection nebula NGC 1977. We

employed Herschel far-infrared photometric images to determine dust

properties. Moreover, we compared with Spitzer mid-infrared photometry

to trace hot dust and large molecules, and velocity-resolved IRAM 30m

CO(2-1) observations of the molecular gas. Results: The [C II]

intensity is tightly correlated with PAH emission in the IRAC 8 μm

band and far-infrared emission from warm dust, with small variations

between the four studied subregions (Veil Shell, OMC4, M43, and NGC

1977). The correlation between [C II] and CO(2-1) is very different in

the four subregions and is very sensitive to the detailed geometry of

the respective regions. Constant-density PDR models are able to

reproduce the observed [C II], CO(2-1), and integrated far-infrared

(FIR) intensities. The physical conditions in the Veil Shell of the

Orion Nebula, M43, and NGC 1977 reveal a constant ratio of thermal

pressure pth over incident FUV radiation field measured by

G0. We observe strong variations in the photoelectric heating

efficiency in the Veil Shell behind the Orion Bar and these variations

are seemingly not related to the spectral properties of the PAHs.

Conclusions: The [C II] emission from the Orion Nebula complex stems

mainly from moderately illuminated PDR surfaces. The correlations of the

different tracers ([C II], FIR, CO, 70 μm, and 8 μm emission) show

small variations that are not yet understood. Future observations with

the James Webb Space Telescope can shine light on the PAH properties

that may be linked to these variations.

Organisation(en)

Institut für Astrophysik

Externe Organisation(en)

Leiden University, Spanish National Research Council (CSIC), Telespazio Vega UK Ltd., Université de Toulouse, University of Maryland, College Park, Universität zu Köln, NASA Ames Research Center, Max-Planck-Institut für Radioastronomie, Institut de RadioAstronomie Millimétrique (IRAM)

Journal

Astronomy & Astrophysics

Band

658

ISSN

0004-6361

DOI

https://doi.org/10.1051/0004-6361/202140805

Publikationsdatum

02-2022

Peer-reviewed

Ja

ÖFOS 2012

103004 Astrophysik, 103003 Astronomie

Schlagwörter

ASJC Scopus Sachgebiete

Astronomy and Astrophysics, Space and Planetary Science

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/3fb9bfc0-9a1c-486b-b612-f63887275cb1