The effects of different cooling and heating function models on a simulated analog of NGC300

TL;DR

This study compares two approximation methods for gas cooling and heating in galaxy simulations, revealing that machine learning provides more accurate and systematically hotter temperature predictions for low-density gas, with implications for observable emission rates.

Contribution

It introduces a machine learning-based approximation scheme for gas cooling/heating, improving accuracy over traditional polynomial interpolation methods in galaxy simulations.

Findings

Machine learning approximation yields systematically hotter low-density gas.

Phase diagrams differ most near a critical temperature-density curve.

Slight differences in CII emission rates between the two methods.

Abstract

Gas cooling and heating rates are vital components of hydrodynamic simulations. However, they are computationally expensive to evaluate exactly with chemical networks or photoionization codes. We compare two different approximation schemes for gas cooling and heating in an idealized simulation of an isolated galaxy. One approximation is based on a polynomial interpolation of a table of Cloudy calculations, as is commonly done in galaxy formation simulations. The other approximation scheme uses machine learning for the interpolation instead on an analytic function, with improved accuracy. We compare the temperature-density phase diagrams of gas from each simulation run to assess how much the two simulation runs differ. Gas in the simulation using the machine learning approximation is systematically hotter for low-density gas with $-3 \lesssim \log{(n_b/\mathrm{cm}^{-3})} \lesssim -1$. We find a critical curve in the phase diagram where the two simulations have equal amounts of gas. The phase diagrams differ most strongly at temperatures just above and below this critical curve. We compare CII emission rates for collisions with various particles (integrated over the gas distribution function), and find slight differences between the two simulations. Future comparisons with simulations including radiative transfer will be necessary to compare observable quantities like the total CII luminosity.