Large-scale ¹³CO J = 5 → 4 and [C I] Mapping of Orion A

We present maps of the ¹³CO J = 5 → 4 (551 GHz) and [C I] ³P₁ → ³P₀ (492 GHz) emission in the Orion A molecular cloud, covering a 05 × 2^° area. A large velocity gradient (LVG) analysis of ¹³CO J = 5 → 4 and J = 1 → 0 suggests that the gas temperatures in the northern part of OMC-1 (north of Δδ = -20') are ~45 K and are, on average, at least 20 K higher than those to the south. The average ¹³CO column density is log(N/cm^-2) = 16.4 ± 0.3 and is fairly constant throughout the cloud, even in the low-temperature region south of BN/KL. LVG modeling of the [C I] emission shows a typical C⁰ column density of 2 × 10¹⁷ cm^-2, which yields a C/CO abundance ratio in the cloud of ~0.1 (rising to levels in excess of 0.5 at the cloud edges). Comparison of the Δ-variance (which measures spatial structure in a manner similar to a power spectrum) of the Submillimeter Wave Astronomy Satellite [C I], Five College Radio Astronomy Observatory ¹³CO J = 1 → 0, and CS J = 1 → 0 velocity-integrated maps suggests that the [C I] and ¹³CO emission arise from the same gas. In contrast, the CS emission likely originates in gas that is considerably more clumpy.