The Effects Of Local Stellar Radiation And Dust Depletion On Non-equilibrium Interstellar Chemistry

By Keith Cowing
Press Release
August 4, 2022
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The Effects Of Local Stellar Radiation And Dust Depletion On Non-equilibrium Interstellar Chemistry
Stellar spectra in the eight stellar age bins used to track the fluxes from star particles, calculated using starburst99 stellar evolution models. These spectra are used to compute the average photoionisation cross sections in each age bin.

Interstellar chemistry is important for galaxy formation, as it determines the rate at which gas can cool, and enables us to make predictions for observable spectroscopic lines from ions and molecules.

We explore two central aspects of modelling the chemistry of the interstellar medium (ISM): (1) the effects of local stellar radiation, which ionises and heats the gas, and (2) the depletion of metals onto dust grains, which reduces the abundance of metals in the gas phase.

We run high-resolution (400 M⊙ per baryonic particle) simulations of isolated disc galaxies, from dwarfs to Milky Way-mass, using the FIRE galaxy formation models together with the CHIMES non-equilibrium chemistry and cooling module.

In our fiducial model, we couple the chemistry to the stellar fluxes calculated from star particles using an approximate radiative transfer scheme, and we implement an empirical density-dependent prescription for metal depletion. For comparison, we also run simulations with a spatially uniform radiation field, and without metal depletion.

Our fiducial model broadly reproduces observed trends in HI and H2 mass with stellar mass, and in line luminosity versus star formation rate for [CII] 158μm, [OI] 63μm, [OIII] 88μm, [NII] 122μm and Hα 6563A. Our simulations with a uniform radiation field predict fainter luminosities, by up to an order of magnitude for [OIII] 88μm and Hα 6563A, while ignoring metal depletion increases the luminosity of carbon and oxygen lines by a factor ≈2.

However, the overall evolution of the galaxy is not strongly affected by local stellar fluxes or metal depletion, except in dwarf galaxies where the inclusion of local fluxes leads to weaker outflows and hence higher gas fractions.

Alexander J. Richings, Claude-Andre Faucher-Giguere, Alexander B. Gurvich, Joop Schaye, Christopher C. Hayward

Comments: 29 pages, 24 figures (including appendices). Submitted to MNRAS
Subjects: Astrophysics of Galaxies (astro-ph.GA)
Cite as: arXiv:2208.02288 [astro-ph.GA] (or arXiv:2208.02288v1 [astro-ph.GA] for this version)
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Submission history
From: Alexander Richings
[v1] Wed, 3 Aug 2022 18:13:19 UTC (23,323 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) 🖖🏻