2019ApJ...880..133J

We present maps of atomic carbon [C I](³P₁→³P₀) and [C I](³P₂→³P₁) emission (hereafter [C I] (1-0) and [C I] (2-1), respectively) at a linear resolution ∼1 kpc scale for a sample of one H II, six LINER, three Seyfert, and five starburst galaxies observed with the Herschel Space Observatory. We compare spatial distributions of two [C I] lines with that of CO J=1→0 (hereafter CO (1-0)) emission, and find that both [C I] lines distribute similarly to CO (1-0) emission in most galaxies. We present luminosity ratio maps of L_[CI](1–0)^′^/LCO(1-0)_^′^, L_[CI](2–1)^′^/LCO(1-0)_^′^, L_[CI](2–1)^′^/L[CI](1-0)_^′^ (hereafter R_[CI]) and 70-to-160 µm far-infrared color of f₇₀/f₁₆₀. L_[CI](2–1)^′^/LCO(1-0)_^′^, R_[CI] and f₇₀/f₁₆₀ are centrally peaked in starbursts; whereas they remain relatively constant in LINERs, indicating that star-forming activity can enhance carbon emission, especially for [C I] (2-1). We explore the correlations between the luminosities of CO (1-0) and [C I] lines, and find that L_CO(1–0)^′^ correlates tightly and almost linearly with both L_[CI](1–0)^′^ and L_[CI](2–1)^′^, suggesting that [C I] lines, similar to CO (1-0), can trace total molecular gas in H II, LINER, Seyfert, and starburst galaxies on kpc scales. We investigate the dependence of L_[CI](1–0)^′^/LCO(1-0)_^′^, L_[CI](2–1)^′^/LCO(1-0)_^′^ and [C I] excitation temperature, T_ex, on dust temperature, T_dust, and find noncorrelation and a weak and modest correlation, respectively. The ratio of L_[CI](1–0)^′^/LCO(1-0)_^′^ stays a smooth distribution in most galaxies, indicating that the conversion factor of [C I] (1-0) luminosity to H₂ mass (X_[CI](1–0)) changes with CO (1-0) conversion factor (α_CO) proportionally. Under optically thin and local thermodynamical equilibrium assumptions, we derive a galaxy-wide average carbon excitation temperature of T_ex∼19.7±0.5K, and an average neutral carbon abundance of X[CI]/X[H₂]∼2.5±1.0×10^–5 in our resolved sample, which is comparable to the usually adopted value of 3 x 10^–5, but ∼3 times lower than the carbon abundance in local (ultra)luminous infrared galaxies. We conclude that the carbon abundance varies in different galaxy types.