[CII] gas in IC 342

¹ I. Physikalisches Institut der Universität zu Köln, Zülpicher Straße 77, 50937 Köln, Germany
e-mail: roellig@ph1.uni-koeln.de
² Max-Planck-Institut für Radioastronomie, Auf dem Hügel 69, 53121 Bonn, Germany
³ Deutsches Zentrum für Luft- und Raumfahrt, Institut für Planetenforschung, Rutherfordstraße 2, 12489 Berlin, Germany
⁴ Institut für Optik und Atomare Physik, Technische Universität Berlin, Hardenbergstraße 36, 10623 Berlin, Germany
⁵ Max-Planck-Institut für Sonnensystemforschung, Max-Planck-Straße 2, 37191 Katlenburg-Lindau, Germany
⁶ Leiden Observatory, Leiden University, PO Box 9513, 2300 RA Leiden, The Netherlands

Received: 31 January 2012
Accepted: 30 March 2012

Abstract

We used the dual-band receiver GREAT on board the SOFIA airborne telescope to perform observations of the [C II] 158 μm fine-structure line at the postitions of two giant molecular clouds (GMC) in the center of IC 342 (GMCs C and E) and compared the spectra with corresponding ground-based data for low- and mid-J CO and [C I]. We performed model calculations assuming a clumpy photo-dissociation region (PDR) environment using the KOSMA-τ PDR model code to derive physical parameters of the local medium. The [C II] 158 μm emission resembles the spectral signature of ground-based atomic and molecular lines, which indicates a common origin. The emission from GMC E can be decomposed into a cool, molecular component with weak far-ultraviolet (FUV) fields and low, mean densities of 10³ cm^-3 and a strongly excited starburst/PDR region with higher densities of 10⁴ cm^-3 and FUV intensities of 250–300 Draine fields. The emission from GMC C is consistent with gas densities of 5000 cm^-3, FUV intensities of a few Draine fields and total gas masses of 20 × 10⁶ M_⊙. The high spectral resolution of the GREAT receiver allowed us to decompose the [C II] emission of the GMC E into a strongly excited gas component resembling a PDR/starburst environment and a quieter, less excited gas component and to analyze the different components within a single beam individually.