Abstract

Contributed Talk - Splinter LowMet

Friday, 13 September 2024, 15:10   (S23)

The carbon cycle in α-enhanced ISM conditions

Thomas G. Bisbas (1), Zhi-Yu Zhang (2), et al.
(1) Zhejiang Lab, Hangzhou, China; (2) Nanjing University, Nanjing, China

Most current studies conventionally apply linear scaling to all elemental abundances based on the gas-phase metallicity. However, these elements, including carbon and oxygen, are enriched differentially by stellar nucleosynthesis and the overall galactic chemical evolution, evident from α-enhancement in multiple galactic observations such as starbursts, high-redshift star-forming galaxies, and low-metallicity dwarfs. Using 3D-PDR, we perform astrochemical modelling to simulate the impact of an α-enhanced ISM gas cloud on the abundances of the three phases of carbon (C+, C, CO) dubbed as 'the carbon cycle'. We vary the cosmic-ray ionization rate and the FUV intensity in a three-dimensional star-forming cloud, mimicking the ISM conditions of different galaxy types. In galaxies with [C/O]<0, CO, C, and C+, all decrease in both abundances and emission, though with differential biases. The low-J CO emission is found to be the most stable tracer for the molecular gas, while C and C+ trace H2 gas only under limited conditions, in line with recent discoveries of [CI]-dark galaxies. Using the PDFchem algorithm, we extent our study by investigating the utility of [CII]158μm, [CI](1-0) and CO(1-0) lines in tracing the cold H2 gas in low-metallicity ISM conditions, assuming various column density probability distribution functions.