Photon dominated regions in NGC 3603

[CI] and mid-J CO line emission

¹ I. Physikalisches Institut, Universität zu Köln, Zülpicher Str. 77, 50937 Köln, Germany
e-mail: roellig@ph1.uni-koeln.de
² Instituto de Radioastronomia Milimetrica (IRAM), Avda. Divina Pastora 7, 18012 Granada, Spain
³ Department of Physics, Faculty of Science, Hokkaido University, N10W8, Kita-ku, Sapporo 060-0810, Japan
⁴ SRON Netherlands Institute for Space Research, PO Box 800, 9700 AV Groningen, The Netherlands
⁵ National Radio Astronomy Observatory. 520 Edgemont Road, Charlottesville, VA 22903, USA
⁶ Argelander-Institut für Astronomie, Universität Bonn, Auf dem Hügel 71, 53121 Bonn, Germany
⁷ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
⁸ Department of Physical Science, Osaka Prefecture University, Gakeun 1-1, Sakai, Osaka 599-8531, Japan
⁹ Department of Astrophysics, Nagoya University, Furocho, Chikusaku, Nagoya 464-8602, Japan
¹⁰ Deutsches SOFIA Institut, Universität Stuttgart, Pfaffenwaldring 31, 70569 Stuttgart, Germany
¹¹ Seoul National University, Seoul 151-742, Korea
¹² ALMA-J Project Office, National Astronomical Observatory of Japan, 2-21-1 Osawa, Mitaka, Tokyo 181-8588, Japan
¹³ Jet Propulsion Laboratory, M/S 169-507, 4800 Oak Grove Drive, Pasadena, CA 91109, USA
¹⁴ European Southern Observatory, Alonso de Cordova 3107, Vitacura, Casilla 19001, Santiago, Chile

Received: 11 April 2010
Accepted: 13 September 2010

Abstract

Aims. We aim at deriving the excitation conditions of the interstellar gas as well as the local FUV intensities in the molecular cloud surrounding NGC 3603 to get a coherent picture of how the gas is energized by the central stars.

Methods. The NANTEN2-4 m submillimeter antenna is used to map the [CI] 1–0, 2–1 and CO 4–3, 7–6 lines in a 2′ × 2′ region around the young OB cluster NGC 3603 YC. These data are combined with C¹⁸O 2–1 data, HIRES-processed IRAS 60 μm and 100 μm maps of the FIR continuum, and Spitzer/IRAC maps.

Results. The NANTEN2 observations show the presence of two molecular clumps located south-east and south-west of the cluster and confirm the overall structure already found by previous CS and C¹⁸O observations. We find a slight position offset of the peak intensity of CO and [CI], and the atomic carbon appears to be further extended compared to the molecular material. We used the HIRES far-infrared dust data to derive a map of the FUV field heating the dust. We constrain the FUV field to values of χ = 3−6 × 10³ in units of the Draine field across the clouds. Approximately 0.2 to 0.3% of the total FUV energy is re-emitted in the [CII] 158 μm cooling line observed by ISO. Applying LTE and escape probability calculations, we derive temperatures (T_MM1 = 43 K, T_MM2 = 47 K), column densities (N_MM1 = 0.9 × 10²² cm^-2, N_MM2 = 2.5 × 10²² cm^-2) and densities (n_MM1 = 3 × 10³ cm^-3, n_MM2 = 10³−10⁴ cm^-3) for the two observed molecular clumps MM1 and MM2.

Conclusions. The cluster is strongly interacting with the ambient molecular cloud, governing its structure and physical conditions. A stability analysis shows the existence of gravitationally collapsing gas clumps which should lead to star formation. Embedded IR sources have already been observed in the outskirts of the molecular cloud and seem to support our conclusions.