2008A&A...489..207S

In this paper we discuss the physical conditions of clumpy nature in the IC348 molecular cloud. We show that the millimeter and sub-millimeter line emission from the IC348 molecular cloud can be modelled as originating from a photon dominated region (PDR). We combine new observations of fully sampled maps in [CI] at 492GHz and ¹²CO 4-3, taken with the KOSMA 3m 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 [CI] ³P₁-³P₀/¹²CO 4-3, [CI]³P₁-³P₀/¹³CO 1-0, and ¹²CO 4-3/¹²CO 1-0. A first rough estimate of abundance is obtained from an LTE analysis. To understand the [CI] and CO emission from the PDRs in IC348, 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. We provide detailed fits to observations at seven representative positions in the cloud, revealing clump densities between 4x10⁴cm^–3 and 4x10⁵cm^–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.