南方基地知识库

Using the atomic carbon [CI](P-3(1) -> 3P(0)) and [CI](P-3(2) -> P-3(1)) emission {hereafter [Ci](1 - 0) and [Ci](2 - 1), respectively} maps observed with the HerschelSpaceObservatory, and CO(1 - 0), Hi, infrared and submm maps from literatures, we estimate the [CI]-to-H-2 and CO-to-H-2 conversion factors of alpha([CI](1 - 0)), alpha([CI](2 - 1)), and alpha(CO) at a linear resolution kpc scale for six nearby galaxies of M 51, M 83, NGC 3627, NGC 4736, NGC 5055, and NGC 6946. This is perhaps the first effort, to our knowledge, in calibrating both [CI]-to-H-2 conversion factors across the spiral disks at spatially resolved kpc scale though such studies have been discussed globally in galaxies near and far. In order to derive the conversion factors and achieve these calibrations, we adopt three different dust-to-gas ratio (DGR) assumptions that scale approximately with metallicity taken from precursory results. We find that for all DGR assumptions, the alpha([CI](1 - 0)), alpha([CI](2 - 1)), and alpha(CO) are mostly flat with galactocentric radii, whereas both alpha([CI](2 - 1)) and alpha(CO) show decrease in the inner regions of galaxies. And the central alpha(CO) and alpha([CI](2 - 1)) values are on average similar to 2.2 and 1.8 times lower than its galaxy averages. The obtained carbon abundances from different DGR assumptions show flat profiles with galactocentric radii, and the average carbon abundance of the galaxies is comparable to the usually adopted value of 3 x 10(-5). We find that both metallicity and infrared luminosity correlate moderately with the alpha(CO), whereas only weakly with either the alpha([CI](1 - 0)) or carbon abundance, and not at all with the alpha([CI](2 - 1)).