Modeling CO Line Luminosity Using FIRE Simulations: I. Methodology and Validation of Molecular Gas and CO Abundance
Abstract
We present a post-processing pipeline that predicts CO line luminosities, molecular hydrogen masses, and CO abundances for galaxies in the Feedback in Realistic Environments (FIRE-2) simulations, as a first step toward CO response functions for line intensity mapping mocks. SKIRT gives the radiation field reaching each gas cell. CLOUDY, tabulated on a five-parameter grid (metallicity, density, turbulent velocity, radiation field, cloud scale) and interpolated, gives L'CO(1−0) and the H2 and CO masses. In this first of three papers we validate the pipeline against observations. For Milky Way (MW) molecular clouds, the predicted L'CO(1−0) rises sharply at AV∼1 and matches the observed values above that column. For a uniform 3 Z⊙ the summed luminosity is within 35\% of the observed total. A factor of three increase in metallicity changes the total L'CO(1−0) by an order of magnitude. Along MW sight lines, the predicted NCO/NH2 reproduces the observed upturn within 0.3 dex in NH2 but falls below the data at higher columns. At z=0 our molecular gas masses agree with xCOLD GASS for SFR≳0.3 M⊙ yr−1 and are converged across our simulation resolutions. At z≳1 observed gas masses exceed ours at fixed stellar mass, though selection effects and conversion-factor assumptions limit this comparison. CO luminosities are compared with extragalactic observations in Paper II. Capturing the metallicity-dependent dust shielding of CO from photodissociation is essential for modeling CO emission in low-mass and high-redshift galaxies.
Related
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BibTeX
@misc{tolgay2026modeling,
title = {{Modeling CO Line Luminosity Using FIRE Simulations: I. Methodology and Validation of Molecular Gas and CO Abundance}},
author = {Doğa Tolgay and Norman W. Murray and Dongwoo Chung and J. Richard Bond and Nathan J. Carlson and Robert Feldmann and Andrew Wetzel and Guochao Sun},
howpublished = {arXiv},
year = {2026},
month = oct,
doi = {10.48550/arxiv.2610.12159},
eprint = {2610.12159},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2610.12159},
}
RIS
TY - UNPB
TI - Modeling CO Line Luminosity Using FIRE Simulations: I. Methodology and Validation of Molecular Gas and CO Abundance
AU - Doğa Tolgay
AU - Norman W. Murray
AU - Dongwoo Chung
AU - J. Richard Bond
AU - Nathan J. Carlson
AU - Robert Feldmann
AU - Andrew Wetzel
AU - Guochao Sun
PY - 2026
DA - 2026/10/08
PB - arXiv
DO - 10.48550/arxiv.2610.12159
UR - https://arxiv.org/abs/2610.12159
AB - We present a post-processing pipeline that predicts CO line luminosities, molecular hydrogen masses, and CO abundances for galaxies in the Feedback in Realistic Environments (FIRE-2) simulations, as a first step toward CO response functions for line intensity mapping mocks. SKIRT gives the radiation field reaching each gas cell. CLOUDY, tabulated on a five-parameter grid (metallicity, density, turbulent velocity, radiation field, cloud scale) and interpolated, gives L'_CO(1−0) and the H_2 and CO masses. In this first of three papers we validate the pipeline against observations. For Milky Way (MW) molecular clouds, the predicted L'_CO(1−0) rises sharply at A_V∼1 and matches the observed values above that column. For a uniform 3 Z_⊙ the summed luminosity is within 35\% of the observed total. A factor of three increase in metallicity changes the total L'_CO(1−0) by an order of magnitude. Along MW sight lines, the predicted N_CO/N_H_2 reproduces the observed upturn within 0.3 dex in N_H_2 but falls below the data at higher columns. At z=0 our molecular gas masses agree with xCOLD GASS for SFR≳0.3 M_⊙ yr^−1 and are converged across our simulation resolutions. At z≳1 observed gas masses exceed ours at fixed stellar mass, though selection effects and conversion-factor assumptions limit this comparison. CO luminosities are compared with extragalactic observations in Paper II. Capturing the metallicity-dependent dust shielding of CO from photodissociation is essential for modeling CO emission in low-mass and high-redshift galaxies.
ER -