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Title: Tracing Molecular Gas Mass in z ≃ 6 Galaxies with [C ii]
Abstract

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 11,125z≃ 6 star-forming, main-sequence galaxies from thesimbasimulations, with line emission modeled by the Simulator of Galaxy Millimeter/Submillimeter Emission. 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 sublinear (slope 0.78 ± 0.01)logL[CII]logMmolrelation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies atz≲ 6. We derive a median [Cii]-to-Mmolconversion factor ofα[CII]≃ 18M/L. This is lower than the average value of ≃30M/Lderived 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 COJ= 1–0, especially at the lowest metallicities, where much of the gas isCO-dark. We find thatL[CII]is more tightly correlated withMmolthan with star formation rate (SFR), and both thelogL[CII]logMmolandlogL[CII]logSFRrelations arise from the Kennicutt–Schmidt relation. Our findings suggest thatL[CII]is a promising tracer of the molecular gas at the earliest cosmic epochs.

 
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Award ID(s):
1909153 2005578
NSF-PAR ID:
10486208
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ;
Publisher / Repository:
DOI PREFIX: 10.3847
Date Published:
Journal Name:
The Astrophysical Journal
Volume:
929
Issue:
1
ISSN:
0004-637X
Format(s):
Medium: X Size: Article No. 92
Size(s):
["Article No. 92"]
Sponsoring Org:
National Science Foundation
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