Clumpy photon-dominated regions in Carina

I. [C I] and mid-J CO lines in two 4'4' fields

¹ KOSMA, I. Physikalisches Institut, Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany e-mail: kramer@ph1.uni-koeln.de
² Argelander-Institut für Astronomie, Auf dem Hügel 71, 53121 Bonn, Germany
³ Department of Physical Science, Osaka Prefecture University, Osaka 599-8531, Japan
⁴ Departamento de Astronomía, Universidad de Chile, Casilla 36-D, Santiago, Chile
⁵ Department of Astrophysics, Nagoya University, Chikusa-ku, Nagoya 464-8602, Japan
⁶ Seoul National University, Seoul 151-742, Korea

Received: 8 May 2007
Accepted: 29 October 2007

Abstract

Context.The Carina region is an excellent astrophysical laboratory for studying the feedback mechanisms of newly born, very massive stars within their natal giant molecular clouds (GMCs) at only 2.35 kpc distance.

Aims.We use a clumpy PDR model to analyse the observed intensities of atomic carbon and CO and to derive the excitation conditions of the gas.

Methods.The NANTEN2-4 m submillimeter telescope was used to map the [C I] ³P₁-³P₀, ³P₂-³P₁ and CO 4–3, 7–6 lines in two 4'4' regions of Carina where molecular material interfaces with radiation from the massive star clusters. One region is the northern molecular cloud near the compact OB cluster Tr 14, and the second region is in the molecular cloud south of η Car and Tr 16. These data were combined with ¹³CO SEST spectra, HIRES/IRAS 60 μm and 100 μm maps of the FIR continuum, and maps of 8 μm IRAC/Spitzer and MSX emission.

Results.We used the HIRES far-infrared dust data to create a map of the FUV field heating the gas. The northern region shows an FUV field of a few 10³ in Draine units while the field of the southern region is about a factor 10 weaker. While the IRAC 8m emission lights up at the edges of the molecular clouds, CO and also [C I] appear to trace the H₂ gas column density. The northern region shows a complex velocity and spatial structure, while the southern region shows an edge-on PDR with a single Gaussian velocity component. We constructed models consisting of an ensemble of small spherically symmetric PDR clumps within the  beam (0.43 pc), which follow canonical power-law mass and mass-size distributions. We find that an average local clump density of 210⁵ cm^-3 is needed to reproduce the observed line emission at two selected interface positions.

Conclusions.Stationary, clumpy PDR models reproduce the observed cooling lines of atomic carbon and CO at two positions in the Carina Nebula.