EDP Sciences
Free access
Volume 423, Number 2, August IV 2004
Page(s) 579 - 592
Section Interstellar and circumstellar matter
DOI http://dx.doi.org/10.1051/0004-6361:20041063

A&A 423, 579-592 (2004)
DOI: 10.1051/0004-6361:20041063

Origin of diffuse C II 158 micron and Si II 35 micron emission in the Carina nebula

M. Mizutani1, T. Onaka1 and H. Shibai2, 3

1  Department of Astronomy, Graduate School of Science, University of Tokyo, Tokyo 113-0033, Japan
    e-mail: onaka@astron.s.u-tokyo.ac.jp
2  Division of Particle and Astrophysical Science, Graduate School of Science, Nagoya University, Nagoya 464-8602, Japan
3  Institute of Advanced Research (IAR), Nagoya University, Nagoya 464-8602, Japan

(Received 26 August 2003 / Accepted 11 May 2004)

We present the results of mapping observations with ISO of [ $\ion{O}{i}$] 63  $\mu$m, 145  $\mu$m, [ $\ion{N}{ii}$] 122  $\mu$m, [ $\ion{C}{ii}$] 158  $\mu$m, [ $\ion{Si}{ii}$] 35  $\mu$m, and H 2 9.66  $\mu$m line emissions for the Carina nebula, an active star-forming region in the Galactic plane. The observations were made for the central $40\arcmin \times 20\arcmin$ area of the nebula, including the optically bright $\ion{H}{ii}$ region and molecular cloud lying in front of the ionized gas. Around the center of the observed area is the interface between the $\ion{H}{ii}$ region and the molecular cloud which creates a typical photodissociation region (PDR). The [ $\ion{C}{ii}$] 158  $\mu$m emission shows a good correlation with the [ $\ion{O}{i}$] 63  $\mu$m emission and peaks around the $\ion{H}{ii}$-molecular region interface. The correlated component has the ratio of [ $\ion{C}{ii}$] 158  $\mu$m to [ $\ion{O}{i}$] 63  $\mu$m of about 2.8. We estimate from the correlation that about 80% of [ $\ion{C}{ii}$] emission comes from the PDR in the Carina nebula. The photoelectric heating efficiency estimated from the ratio of the ([ $\ion{C}{ii}$] 158  $\mu$m + [ $\ion{O}{i}$] 63  $\mu$m) intensity to the total far-infrared intensity ranges from 0.06 to 1.2%. [ $\ion{O}{i}$] 145  $\mu$m is detected marginally at 10 positions. The average ratio of [ $\ion{O}{i}$] 145  $\mu$m to [ $\ion{O}{i}$] 63  $\mu$m of these positions is about $0.09 \pm 0.01$ and is larger than model predictions. The observed [ $\ion{C}{ii}$] 158  $\mu$m to [ $\ion{O}{i}$] 63  $\mu$m ratio indicates a relatively low temperature ( < 500 K) of the gas, while the large [ $\ion{O}{i}$] 145  $\mu$m to 63  $\mu$m ratio suggests a high temperature (~ 1000 K). This discrepancy cannot be accounted for consistently by the latest PDR model with the efficient photoelectric heating via polycyclic aromatic hydrocarbons (PAHs) even if absorption of [ $\ion{O}{i}$] 63  $\mu$m by foreground cold gas is taken into account. We suggest that absorption of [ $\ion{C}{ii}$] 158  $\mu$m together with [ $\ion{O}{i}$] 63  $\mu$m by overlapping PDRs, in which the heating via PAHs is suppressed due to the charge-up effect, may resolve the discrepancy. Quite strong [ $\ion{Si}{ii}$] 35  $\mu$m emission has been detected over the observed area. It shows a good correlation with [ $\ion{N}{ii}$] 122  $\mu$m, but the correlation with [ $\ion{O}{i}$] 63  $\mu$m is very weak, indicating that [ $\ion{Si}{ii}$] 35  $\mu$m comes mainly from the diffuse ionized gas rather than the PDR. The ratio of [ $\ion{Si}{ii}$] 35  $\mu$m to [ $\ion{N}{ii}$] 122  $\mu$m is about 8 and Si of about 50% of the solar abundance relative to  N should be present in the gas phase. The present results suggest that efficient dust destruction takes place and a large fraction of Si returns to the gas in the Carina star-forming region.

Key words: infrared: ISM -- ISM: abundances -- ISM: individual objects: Carina nebula -- ISM: lines and bands -- ISM: dust, extinction

SIMBAD Objects
Tables at the CDS

© ESO 2004

What is OpenURL?

The OpenURL standard is a protocol for transmission of metadata describing the resource that you wish to access.

An OpenURL link contains article metadata and directs it to the OpenURL server of your choice. The OpenURL server can provide access to the resource and also offer complementary services (specific search engine, export of references...). The OpenURL link can be generated by different means.

  • If your librarian has set up your subscription with an OpenURL resolver, OpenURL links appear automatically on the abstract pages.
  • You can define your own OpenURL resolver with your EDPS Account.
    In this case your choice will be given priority over that of your library.
  • You can use an add-on for your browser (Firefox or I.E.) to display OpenURL links on a page (see http://www.openly.com/openurlref/). You should disable this module if you wish to use the OpenURL server that you or your library have defined.