Mapping of large scale 158  [CII] line emission: Orion A

¹ Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai (Bombay) 400 005, India
² Joint Astronomy Programme, Dept. of Physics, Indian Institute of Science, Bangalore 560 012, India
³ I. Physikalisches Institut, Universität zu Köln, Zülpicher Strasse 77, 50937 Köln, Germany
⁴ Institute of Space and Astronautical Science, Kanagawa 229, Japan
⁵ Instituto Nacional de Astrofisica, Optica y Electronica, Tonantzintla, Puebla 72840, Mexico
⁶ Dept. of Physics, Nagoya University, Nagoya 464, Japan

Corresponding author: B. Mookerjea, bhaswati@ph1.uni-koeln.de

Received: 4 November 2002
Accepted: 6 April 2003

Abstract

We present the first results of an observational programme undertaken to map the fine structure line emission of singly ionized carbon ([CII] 157.7409 ) over extended regions using a Fabry Perot spectrometer newly installed at the focal plane of a 100 cm balloon-borne far-infrared telescope. This new combination of instruments has a velocity resolution of ~200 km s^-1 and an angular resolution of 1 5. During the first flight, an area of 30´´  in Orion A was mapped. These observations extend over a larger area than previous observations, the map is fully sampled and the spectral scanning method used enables reliable estimation of the continuum emission at frequencies adjacent to the [CII] line. The total [CII] line luminosity, calculated by considering up to 20% of the maximum line intensity is 0.04% of the luminosity of the far-infrared continuum. We have compared the [CII] intensity distribution with the velocity-integrated intensity distributions of ¹³CO(1-0), CI(1-0) and CO(3-2) from the literature. Comparison of the [CII], [CI] and the radio continuum intensity distributions indicates that the largescale [CII] emission originates mainly from the neutral gas, except at the position of M 43, where no [CI] emission corresponding to the [CII] emission is seen. Substantial part of the [CII] emission from here originates from the ionized gas. 
The observed line intensities and ratios have been analyzed using the PDR models by [CITE] to derive the incident UV flux and volume density at a few selected positions. The models reproduce the observations reasonably well at most positions excepting the [CII] peak (which coincides with the position of Ori C). Possible reason for the failure could be the simplifying assumption of a homogeneous plane parallel slab in place of a more complicated geometry.