The Carbon-to-H2, CO-to-H2 conversion factors, and carbon abundance on kiloparsec scales in nearby galaxies

ABSTRACT Using the atomic carbon [C i] ($^{3} \rm P_{1} \rightarrow {\rm ^3 P}_{0}$) and [C i] ($^{3} \rm P_{2} \rightarrow {\rm ^3 P}_{1}$) emission {hereafter [C i] (1 − 0) and [C i] (2 − 1), respectively} maps observed with the Herschel Space Observatory, and CO (1 − 0), H i, infrared and submm maps from literatures, we estimate the [C i]-to-H2 and CO-to-H2 conversion factors of α[C i](1 − 0), α[C i](2 − 1), and αCO at a linear resolution $\sim 1\,$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 [C i]-to-H2 conversion factors across the spiral disks at spatially resolved $\sim 1\,$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 α[C i](1 − 0), α[C i](2 − 1), and αCO are mostly flat with galactocentric radii, whereas both α[C i](2 − 1) and αCO show decrease in the inner regions of galaxies. And the central αCO and α[C i](2 − 1) values are on average ∼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 × 10−5. We find that both metallicity and infrared luminosity correlate moderately with the αCO, whereas only weakly with either the α[C i](1 − 0) or carbon abundance, and not at all with the α[C i](2 − 1).

Atomic carbon [C i](3P1–3P0) mapping of the nearby galaxy M 83

Atomic carbon (C i) has been proposed to be a global tracer of the molecular gas as a substitute for CO, however, its utility remains unproven. To evaluate the suitability of C i as the tracer, we performed [C i](3P1–3P0) [hereinafter [C i](1–0)] mapping observations of the northern part of the nearby spiral galaxy M 83 with the Atacama Submillimeter Telescope Experiment (ASTE) telescope and compared the distributions of [C i](1–0) with CO lines [CO(1–0), CO(3–2), and 13CO(1–0)], H i, and infrared (IR) emission (70, 160, and 250 μm). The [C i](1–0) distribution in the central region is similar to that of the CO lines, whereas [C i](1–0) in the arm region is distributed outside the CO. We examined the dust temperature, Tdust, and dust mass surface density, Σdust, by fitting the IR continuum-spectrum distribution with a single-temperature modified blackbody. The distribution of Σdust shows a much better consistency with the integrated intensity of CO(1–0) than with that of [C i](1–0), indicating that CO(1–0) is a good tracer of the cold molecular gas. The spatial distribution of the [C i] excitation temperature, Tex, was examined using the intensity ratio of the two [C i] transitions. An appropriate Tex at the central, bar, arm, and inter-arm regions yields a constant [C]$/$[H2] abundance ratio of ∼7 × 10−5 within a range of 0.1 dex in all regions. We successfully detected weak [C i](1–0) emission, even in the inter-arm region, in addition to the central, arm, and bar regions, using spectral stacking analysis. The stacked intensity of [C i](1–0) is found to be strongly correlated with Tdust. Our results indicate that the atomic carbon is a photodissociation product of CO, and consequently, compared to CO(1–0), [C i](1–0) is less reliable in tracing the bulk of “cold” molecular gas in the galactic disk.

The role of atomic carbon in directing electrochemical CO(2) reduction to multicarbon products

Atomic carbon plays a role in steering selectivity in electrochemical carbon mono-/dioxide reduction. Appropriate binding strengths of CO and C, combined with four-fold sites, constitute fundamental features toward selective multicarbon production.

Объемные и поверхностные эффекты при образовании и разрушении графена на родии

Growth and destruction of graphene islands on Rh have been studied accounting processes on the surface and in the substrate bulk simultaneously. Atomic carbon was shown to be distributed between three equilibrium phases: graphene, solid solution in the metal substrate, and chemisorbed carbon. An increase in graphene island area results in corresponding increase in carbon concentration in the solid solution and chemisorbed phase. Atomic carbon concentrations are measured for all three phases for various stages of graphene growth and decomposition. The activation energy of atomic carbon detachment from the graphene island perimeter on Rh has been determined, Edet = 2.7 eV. Surface concentration of graphene islands has been estimated to be about 1010 per сm2.