Issue |
A&A
Volume 489, Number 1, October I 2008
|
|
---|---|---|
Page(s) | 207 - 216 | |
Section | Interstellar and circumstellar matter | |
DOI | https://doi.org/10.1051/0004-6361:20078431 | |
Published online | 23 July 2008 |
The photon dominated region in the IC 348 molecular cloud
1
I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany e-mail: kefeng@ph1.uni-koeln.de
2
SRON Netherlands Institut for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
3
Department of Astronomy & Astrophysics, Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400 005, India
4
Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
Received:
7
August
2007
Accepted:
17
July
2008
Aims. In this paper we discuss the physical conditions of clumpy nature in the IC 348 molecular cloud. We show that the millimeter and sub-millimeter line emission from the IC 348 molecular cloud can be modelled as originating from a photon dominated region (PDR).
Methods. We combine new observations of fully sampled maps in [C I] at 492 GHz and 12CO 4–3, taken with the KOSMA 3 m telescope at about 1´ resolution, with FCRAO data of
12CO 1–0, 13CO 1–0 and far-infrared continuum data observed by HIRES/IRAS.
To derive the physical parameters of the region we analyze the line ratios of
[C I] 3P1–3PCO 4–3,
[C I]3P1–3P
CO 1–0, and 12CO 4–3/12CO 1–0.
A first rough estimate of abundance is obtained from an LTE analysis. To understand the
[C I] and CO emission from the PDRs in IC 348, we use a clumpy PDR model. With an
ensemble of identical clumps, we constrain the total mass from the observed absolute intensities. Then we apply a more realistic clump distribution model with a power law index of 1.8 for clump-mass spectrum and a power law index of 2.3 for mass-size relation.
Results. We provide detailed fits to observations at seven representative positions in the
cloud, revealing clump densities between 4 104 cm-3 and
4
105 cm-3 and C/CO column density ratios between 0.02 and 0.26.
The derived FUV flux from the model fit is consistent with the field calculated from FIR
continuum data, varying between 2 and 100 Draine units across the cloud. We find that
both an ensemble of identical clumps and an ensemble with a power law clump mass distribution produce line intensities which are in good agreement (within a factor ~ 2) with
the observed intensities. The models confirm the anti-correlation between the C/CO abundance ratio and the hydrogen column density found in many regions.
Key words: ISM: clouds / ISM: dust, extinction / ISM: structure / ISM: individual objects: IC 348
© ESO, 2008
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