A Framework for Modeling Polycyclic Aromatic Hydrocarbon Emission in Galaxy Evolution Simulations

Abstract

We present a new methodology for simulating mid-infrared emission from polycyclic aromatic hydrocarbons (PAHs) in galaxy evolution simulations. To do this, we combine theoretical models of PAH emission features as they respond to varying interstellar radiation fields, grain-size distributions, and ionization states with a new model for dust evolution in galaxy simulations. We apply these models to three idealized arepo galaxy evolution simulations within the smuggle physics framework. We use these simulations to develop numerical experiments investigating the buildup of PAH masses and luminosities in galaxies in idealized analogs of the Milky Way, a dwarf galaxy, and a starburst disk. Our main results are as follows. Galaxies with high specific star formation rates have increased feedback energy per unit mass, and are able to shatter grains efficiently, driving up the fraction of ultrasmall grains. At the same time, in our model large radiation fields per unit gas density convert aliphatic grains into aromatics. The fraction of dust grains in the form of PAHs (q PAH) can be understood as a consequence of these processes, and in our model PAHs form primarily from interstellar processing (shattering) of larger grains rather than from the growth of smaller grains. We find that the hardness of the radiation field plays a larger role than variations in the grain-size distribution in setting the total integrated PAH luminosities, though cosmological simulations are necessary to investigate fully the complex interplay of processes that drive PAH band luminosities in galaxies.

An ALMA Spectroscopic Survey of the Brightest Submillimeter Galaxies in the SCUBA-2-COSMOS Field (AS2COSPEC): Physical Properties of z = 2–5 Ultra- and Hyperluminous Infrared Galaxies

“…We set a wide tolerance of q PAH due to the fact that the observed 24 μm is located at the redshifted PAH emission region so that the 24 μm is sensitive to the PAH emission strength. Recent results from simulations also suggest a wide range of q PAH (Narayanan et al 2023).…”

Cosmic Sands. II. Challenges in Predicting and Measuring High-z Dust Temperatures

“…Specifically, we do not model an evolving grain-size distribution in SIMBA, which could significantly change the thermodynamics of the ISM in these galaxies and drive changes in the ways dust absorbs and emits as a function of wavelength. It is known that dust of differing grain sizes have different optical properties and thus dominate galaxy spectra at different wavelengths; e.g., PAHs with grain sizes ∼1-10 Å dominate galaxy emission in the near-to mid-IR (e.g., Narayanan et al 2023). While we cannot test the impact of galaxy dust grain size distributions and how this manifests in IR SEDs, we predict that the addition of a self-consistent grain size evolution model, resulting in nonuniversal dust optical properties and perhaps a wider diversity in FIR SED shapes, would result in greater uncertainties in the inferred dust temperatures from modified blackbody fits to FIR SEDs.…”

GOALS-JWST: Small Neutral Grains and Enhanced 3.3 μm PAH Emission in the Seyfert Galaxy NGC 7469

“…Understanding the physics behind the enhanced durability of the smallest dust particles, which give rise to the excess emission from PAH 3.3 emitters, carries significant implications for simulating the dust mass buildup and chemical enrichment throughout cosmic time (e.g., Narayanan et al 2023). Theoretical studies have shown that molecules consisting of fewer carbon atoms (N c  40) are able to efficiently dissipate the absorbed UV energy via recurrent fluorescence (RF), with a relaxation timescale of ∼milliseconds as opposed to IR emission with timescales of ∼seconds (Leger et al 1988).…”