α-enhanced Astrochemistry: The Carbon Cycle In Extreme Galactic Conditions

By Keith Cowing
Status Report
December 6, 2023
Filed under , , ,
α-enhanced Astrochemistry: The Carbon Cycle In Extreme Galactic Conditions
Left panel: Pairs of [O/H] and [C/O] used in models. Blue circles correspond to models O0C0 and O0C1. Orange squares and green triangles correspond to models O1C0, O1C1, O1C2 according to the assumed D, which is the dust-to-gas ratio normalized to the solar value (see right panel). The horizontal dotted black line (‘Linear’) corresponds to the assumption of a constant [C/O] (equal to −0.07) and independent on [O/H]. The Sharda et al. (2023b,c) (Eqn. 2) cubic-fit, the Nicholls et al. (2017) (Eqn.3) best-fit, and the Garnett et al. (1995) (Eqn.4) best-fit are shown in dot-dashed, dashed, and solid lines, respectively. Small brown diamonds refer to Lyman-continuum leaking galaxies at 𝑧 ∼ 0.3 − 0.4 of Izotov et al. (2023), yellow and dark blue to metal-poor dwarf galaxies of Berg et al. (2016) and Berg et al. (2019), respectively and red to green pea galaxies of Ravindranath et al. (2020). The purple diamond refers to the Isobe et al. (2023) JWST observations of GN-z11. Right panel: Relation of [O/H] versus D. The big blue circle, orange square and green triangle correspond to the values used in our models while their colours are in tandem with those of the left panel. Blue and orange models follow an approximately linear decrease of D as a function of [O/H] and are labeled as ‘D0’. The green triangle has a sub-linear D and is labeled as ‘D1’. Black dotted line corresponds to a linear connection between [O/H] and D to guide the eye. Gray diamonds correspond to the KINGFISH observations of Rémy-Ruyer et al. (2014), while magenta diamonds to the Dwarf Galaxy Survey data of Rémy-Ruyer et al. (2013). — astro-ph.GA

Astrochemistry has been widely developed as a power tool to probe physical properties of the interstellar medium (ISM) in various conditions of the Milky Way (MW) Galaxy, and in near and distant galaxies.

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.

We perform astrochemical modeling 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’. The ISM environmental parameters considered include two cosmic-ray ionization rates (ζCR=10−17 and 10−15s−1), two isotropic FUV radiation field strengths (χ/χ0=1 and 102), and (sub-)linear dust-to-gas relations against metallicity, 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. T

he 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. We call for caution when using [CII]~158μm and Cl as alternative H2-gas tracers for both diffuse and dense gas with non-zero [C/O] ratios.

Thomas G. Bisbas, Zhi-Yu Zhang, Eda Gjergo, Ying-He Zhao, Gan Luo, Donghui Quan, Xue-Jian Jiang, Yichen Sun, Theodoros Topkaras, Di Li, Ziyi Guo

Comments: MNRAS accepted. 21 pages, 15 figures, comments welcome!
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2312.03237 [astro-ph.GA] (or arXiv:2312.03237v1 [astro-ph.GA] for this version)
Submission history
From: Thomas Bisbas Dr.
[v1] Wed, 6 Dec 2023 02:17:02 UTC (5,302 KB)
Astrobiology, Astrochemistry,

Explorers Club Fellow, ex-NASA Space Station Payload manager/space biologist, Away Teams, Journalist, Lapsed climber, Synaesthete, Na’Vi-Jedi-Freman-Buddhist-mix, ASL, Devon Island and Everest Base Camp veteran, (he/him) 🖖🏻