[CII] gas in IC 342

TL;DR

This study uses SOFIA observations to analyze the [C II] 158 μm emission in IC 342's molecular clouds, revealing distinct physical conditions and excitation mechanisms within the clouds.

Contribution

It provides detailed decomposition of [C II] emission into different gas components and applies PDR modeling to derive physical parameters of the local medium.

Findings

GMC E has both a cool, low-density component and a highly excited starburst/PDR region.

GMC C exhibits high gas density and moderate FUV intensity, with a large gas mass.

High spectral resolution enables separation of different gas components within a single beam.

Abstract

Methods: We used the dual-band receiver GREAT on board the SOFIA airborne telescope to perform observations of the [C II] 158 {\mu}m 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-tau PDR model code to derive physical parameters of the local medium. Results: The [C II] 158 {\mu}m 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\times10^6 M$_\odot$. Conclusions: 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.