HYACINTH: HYdrogen And Carbon chemistry In The INTerstellar Medium In Hydro Simulations

By Keith Cowing
Status Report
February 21, 2024
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HYACINTH: HYdrogen And Carbon chemistry In The INTerstellar Medium In Hydro Simulations
Column density maps of different species in the simulated galaxy after post-processing. The total hydrogen and H2 from the simulation are shown in the first two panels. The remaining panels show the column density of H2, C+ , C, and CO obtained via post-processing. The H2 from post-processing (top row, third panel) is remarkably similar to the H2 from the simulation (top row, second panel). CO dominates the carbon budget in the highest NH2 regions and is essentially absent when NH2 ≲ 1021 cm−2 . Atomic carbon traces the full extent of the H2 distribution while C + extends farther out to regions devoid of a significant amount of H2 — astro-ph.GA

Aims. We present a new sub-grid model, HYACINTH — HYdrogen And Carbon chemistry in the INTerstellar medium in Hydro simulations, for computing the non-equilibrium abundances of H2 and its carbon-based tracers, namely CO, C, and C+, in cosmological simulations of galaxy formation.

Methods. The model accounts for the unresolved density structure in simulations using a variable probability distribution function of sub-grid densities and a temperature-density relation. Included is a simplified chemical network tailored for hydrogen and carbon chemistry within molecular clouds and easily integrated into large-scale simulations with minimal computational overhead.

As an example, we apply HYACINTH to a simulated galaxy at redshift z∼2.5 in post-processing and compare the resulting abundances with observations. Results. The chemical predictions from HYACINTH show a good agreement with high-resolution molecular-cloud simulations. We reproduce the HI−H2 transition in the fH2−NH plane for both Milky-Way and LMC-like conditions.

We also match the NCO−NH2 values inferred from absorption measurements towards Milky-Way molecular clouds. Column density maps reveal that CO is concentrated in the peaks of the H2 distribution, while atomic carbon more broadly traces the bulk of H2 in our post-processed galaxy.

Based on surface density profiles of stars and different gas species in the post-processed galaxy, we find that C+ extends farther than all other components and maintains a substantially high surface density out to ∼10kpc. This is similar to the [CII] halos found in some recent observations at high redshifts.

Prachi Khatri, Cristiano Porciani, Emilio Romano-Díaz, Daniel Seifried, Alexander Schäbe

Comments: 16 pages, 8 figures. Submitted to A&A. Comments are welcome
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2402.11023 [astro-ph.GA] (or arXiv:2402.11023v1 [astro-ph.GA] for this version)
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Submission history
From: Prachi Khatri
[v1] Fri, 16 Feb 2024 19:05:27 UTC (1,807 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) 🖖🏻