MID-INFRARED POLYCYCLIC AROMATIC HYDROCARBON AND H{sub 2} EMISSION AS A PROBE OF PHYSICAL CONDITIONS IN EXTREME PHOTODISSOCIATION REGIONS

Journal Article · Fri Nov 20 00:00:00 EST 2009 · Astrophysical Journal (Online)

DOI:https://doi.org/10.1088/0004-637X/706/1/L160· OSTI ID:21378161

Berne, O; Goicoechea, J R ^[1]; Fuente, A ^[2]; Pilleri, P; Joblin, C ^[3]; Gonzalez-GarcIa, M ^[4]

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1. Centro de AstrobiologIa (CSIC/INTA), Laboratiorio de Astrofisica Molecular, Ctra. de Torrejon a Ajalvir, km 4 28850, Torrejon de Ardoz, Madrid (Spain)
2. Observatorio Astronomico Nacional, Apdo. Correos 112, 28803 Alcala de Henares, Madrid (Spain)
3. Universite de Toulouse, UPS, CESR, 9 ave colonel Roche, F-31028 Toulouse cedex 9 (France)
4. LUTH, Observatoire de Paris and Universite Paris, 7 place Jansen, 92190 Meudon (France)

Mid-infrared (mid-IR) observations of polycyclic aromatic hydrocarbons (PAHs) and molecular hydrogen emission are a potentially powerful tool to derive physical properties of dense environments irradiated by intense UV fields. We present new, spatially resolved, Spitzer mid-IR spectroscopy of the high UV field and dense photodissociation region (PDR) around Monoceros R2, the closest ultracompact H II region, revealing the spatial structure of ionized gas, PAHs, and H{sub 2} emissions. Using a PDR model and PAH emission feature fitting algorithm, we build a comprehensive picture of the physical conditions prevailing in the region. We show that the combination of the measurement of PAH ionization fraction and of the ratio between the H{sub 2} 0-0 S(3) and S(2) line intensities, respectively, at 9.7 and 12.3 mum, allows us to derive the fundamental parameters driving the PDR: temperature, density, and UV radiation field when they fall in the ranges T = 250-1500 K, n {sub H} = 10{sup 4}-10{sup 6} cm{sup -3}, and G {sub 0} = 10{sup 3}-10{sup 5}, respectively. These mid-IR spectral tracers thus provide a tool to probe the similar but unresolved UV-illuminated surface of protoplanetary disks or the nuclei of starburst galaxies.

• OSTI ID: 21378161
• Journal Information: Astrophysical Journal (Online), Vol. 706, Issue 1; Other Information: DOI: 10.1088/0004-637X/706/1/L160; ISSN 1538-4357
• Country of Publication: United States
• Language: English

Related Subjects

74 ATOMIC AND MOLECULAR PHYSICS
79 ASTROPHYSICS
COSMOLOGY AND ASTRONOMY
ALGORITHMS
DISSOCIATION
EMISSION
GALAXIES
HYDROGEN
INFRARED SPECTRA
IONIZATION
PHOTOLYSIS
POLYCYCLIC AROMATIC HYDROCARBONS
PROTOPLANETS
ULTRAVIOLET RADIATION
AROMATICS
CHEMICAL REACTIONS
DECOMPOSITION
ELECTROMAGNETIC RADIATION
ELEMENTS
HYDROCARBONS
MATHEMATICAL LOGIC
NONMETALS
ORGANIC COMPOUNDS
PHOTOCHEMICAL REACTIONS
RADIATIONS
SPECTRA