CALIMA: On-the-fly dust and PAH evolution for radiation-hydrodynamics galaxy formation simulations

Abstract

Dust grains and polycyclic aromatic hydrocarbons (PAHs) actively contribute to the thermodynamics, chemistry, and radiative state of the interstellar medium (ISM), yet most ISM models and galaxy simulations either exclude them altogether or adopt simplified treatments. We present CALIMA, a new module for dust and PAH formation and evolution in radiation-hydrodynamics simulations for RAMSES, designed to self-consistently couple dust physics to radiative transfer and non-equilibrium thermochemistry in a multiphase ISM. The model employs a two-size, two-composition dust framework with log-normal grain populations, explicitly evolving stellar dust injection, turbulence-informed gas-phase accretion, shattering, coagulation, thermal and non-thermal sputtering, and shock destruction, while PAHs are separate components with their own evolution. The evolving dust populations and radiation field determine local, wavelength-dependent opacities, photoelectric heating efficiencies, grain-assisted recombination, dust-gas collisional heating/cooling, and H$_2$ formation on both grains and PAHs. Updated treatments of thermal sputtering and collisional cooling that include finite grain sizes and modern ion-solid physics reduce sputtering rates at high temperatures and extend the regime where dust significantly cools hot gas. One-zone ISM tests show that dust and PAH evolution modifies classical thermal phase diagrams and C-bearing chemistry, while isolated disc galaxy simulations reveal environment-dependent variations in dust-to-metal ratio, small-to-large grain ratio, PAH fraction, and interstellar radiation field intensity that drive non-trivial structure in infrared emission, UV transparency, and H$_2$ formation. CALIMA provides a physically motivated framework to interpret dust- and PAH-based observables and to assess dust-mediated feedback in galaxy formation across cosmic time.

Figures (25)

• Figure 1: Overview of the calima model. Click on a process name to jump to its detailed description.
• Figure 2: Underlying grain size distribution assumed within each size bin in the calima model for PAHs, carbonaceous grains and silicate grains. This has been computed for a gas density of $1$ H cm$^{-3}$ and using the DTG for each individual component (PAH, carbonaceous, silicate) of the BARE-GR-S model in Zubko2004InterstellarConstraints.
• Figure 3: Equilibrium grain charge of the small silicate grains ($a=0.005$$\mu$m) under the Mathis1983InterstellarClouds ISRF. Each point describes the charge probability distribution by the mean $\langle Q_{\rm g} \rangle$ (top panel) and width $\sigma_{Q_{\rm g}}$ (bottom panel) at a given value of the charging parameter $\gamma = G_0 \sqrt{T}/n_{\rm e}$. For a fixed $\gamma$, we also vary $T$ between $10$ K and $10^5$ K and $n_{\rm e}$ between $10^{-4}$ and $10^2$ cm$^{-3}$, represented by the colourmap and the size of the point, respectively. The result from the equilibrium modelling by Ibanez-Mejia2019DustMedium is overplotted as solid orange lines, compare to the median of our distribution for neutral ($T<10^4$ K) and ionised gas ($T>10^4$ K).
• Figure 4: Photo-electric net heating efficiency for graphite (blue line) and silicate (brown line) grains embedded in the Mathis1983InterstellarClouds ISRF with the WNM phase conditions. Our modelling is in excellent agreement with the results of Weingartner2001PhotoelectricHeating down to $a\lesssim 100$ Å for graphite grains due to the different choice of optical properties in their work compared to calima.
• Figure 5: Coulomb enhancement factor $F_{\rm C}$ as function of grain size for different ISM phases (CNM, blue; WNM, yellow; WIM, red) assuming a colliding ion with charge $Z_k=1$. Solid-dashed and dotted lines correspond to the results of Weingartner1999InterstellarGrains for silicate and graphite, while solid and dashed correspond to our computed $F_{\rm C}$ for, respectively, silicate and graphite grains. Our results agree reasonably well with Weingartner1999InterstellarGrains, except large deviations for silicate grains (see text for discussion).