FAR-INFRARED DETECTION OF NEUTRAL ATOMIC OXYGEN TOWARD THE HORSEHEAD NEBULA
- Centro de Astrobiologia (CSIC-INTA), Laboratorio de Astrofisica Molecular, Carretera de Ajalvir, Km 4. Torrejon de Ardoz, 28850 Madrid (Spain)
- Canadian Institute for Theoretical Astrophysics, University of Toronto, 60 St. George Street, Toronto, ON M5S 3H8 (Canada)
- Institut d'Astrophysique Spatiale, Universite Paris-Sud, 91405 Orsay Cedex (France)
We present the first detection of the neutral atomic oxygen ({sup 3} P {sub 1}-{sup 3} P {sub 2} fine structure line at {approx}63 {mu}m) toward the Horsehead photodissociation region (PDR). The cloud has been mapped with the Spitzer Space Telescope at far-IR (FIR) wavelengths using the Multiband Imaging Photometer for Spitzer in the spectral energy distribution mode. The [O I]63 {mu}m line peaks at the illuminated edge of the cloud at A{sub V} {approx_equal} 0.1-0.5 (inward the gas becomes too cold and outward the gas density drops). The luminosity carried by the [O I]63 {mu}m line represents a significant fraction of the total FIR dust luminosity (I {sub 63}/I {sub FIR} {approx_equal} 4 x 10{sup -3}). We analyze the dust continuum emission and the nonlocal O I excitation and radiative transfer in detail. The observations are reproduced with a gas density of n {sub H} {approx_equal} 10{sup 4} cm{sup -3} and gas and dust temperatures of T{sub k} {approx_equal} 100 K and T{sub d} {approx_equal} 30 K. We conclude that the determination of the O I {sup 3} P{sub J} level populations and emergent line intensities at such 'low' densities is a complex non-LTE problem. FIR radiative pumping, [O I]63 {mu}m subthermal emission, [O I]145 {mu}m suprathermal and even maser emission can occur and decrease the resulting [O I]63/145 intensity ratio. The Herschel Space Observatory, observing from {approx}55 to 672 {mu}m, will allow us to exploit the diagnostic power of FIR fine structure lines with unprecedented resolution and sensitivity.
- OSTI ID:
- 21313028
- Journal Information:
- Astrophysical Journal (Online), Vol. 699, Issue 2; Other Information: DOI: 10.1088/0004-637X/699/2/L165; Country of input: International Atomic Energy Agency (IAEA); ISSN 1538-4357
- Country of Publication:
- United States
- Language:
- English
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