Abstract / Description of output
We investigate the fine-structure [CII] line at
158μm as a molecular gas tracer by analyzing the relationship between
molecular gas mass (Mmol) and [CII] line
luminosity (L[CII]) in 11,125 z≃6 star-forming, main sequence
galaxies from the SIMBA simulations, with line emission modeled by SÍGAME.
Though most (∼50−100%) of the gas mass in our simulations is ionized,
the bulk (>50%) of the [CII] emission comes from the
molecular phase. We find a sub-linear (slope 0.78±0.01) logL[CII]−logMmol relation, in contrast with the linear relation derived
from observational samples of more massive, metal-rich galaxies at z≲6. We derive a median [CII]-to-Mmol conversion
factor of α[CII]≃18M⊙/L⊙.
This is lower than the average value of ≃30M⊙/L⊙ derived from observations, which we attribute to lower gas-phase
metallicities in our simulations. Thus, a lower, luminosity-dependent,
conversion factor must be applied when inferring molecular gas masses from
[CII] observations of low-mass galaxies. For our
simulations, [CII] is a better tracer of the molecular gas
than CO J=1−0, especially at the lowest metallicities, where much of the gas
is 'CO-dark'. We find that L[CII] is more tightly correlated with
Mmol than with star-formation rate (SFR), and both the logL[CII]−logMmol and logL[CII]−logSFR
relations arise from the Kennicutt-Schmidt relation. Our findings suggest that
L[CII] is a promising tracer of the molecular gas at the earliest
cosmic epochs.
Original language | English |
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Article number | 92 |
Pages (from-to) | 1-13 |
Number of pages | 13 |
Journal | Astrophysical Journal |
Volume | 929 |
Issue number | 1 |
DOIs | |
Publication status | Published - 15 Apr 2022 |
Keywords / Materials (for Non-textual outputs)
- astro-ph.GA