Resolved Neutral Carbon Emission in Nearby Galaxies: [C i] Lines as Total Molecular Gas Tracers

Abstract

Abstract We present maps of atomic carbon [C i]( ) and [C i]( ) 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 (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 / , / , (hereafter ) and 70-to-160 μm far-infrared color of f 70/f 160. / , and 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 correlates tightly and almost linearly with both and , 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 / , / 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 / stays a smooth distribution in most galaxies, indicating that the conversion factor of [C i] (1−0) luminosity to H2 mass ( ) changes with CO (1−0) conversion factor ( ) proportionally. Under optically thin and local thermodynamical equilibrium assumptions, we derive a galaxy-wide average carbon excitation temperature of , and an average neutral carbon abundance of in our resolved sample, which is comparable to the usually adopted value of 3 × 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.