TY - JOUR

T1 - Tracing Molecular Gas Mass in z similar or equal to 6 Galaxies with [C II]

AU - Vizgan, D.

AU - Greve, T. R.

AU - Olsen, K. P.

AU - Zanella, A.

AU - Narayanan, D.

AU - Dave, R.

AU - Magdis, G. E.

AU - Popping, G.

AU - Valentino, F.

AU - Heintz, K. E.

PY - 2022/4/1

Y1 - 2022/4/1

N2 - We investigate the fine-structure [C II] line at 158 mu m as a molecular gas tracer by analyzing the relationship between molecular gas mass (M-mol) and [C II] line luminosity (L-[C (II)]) in 11,125 z similar or equal to 6 star-forming, main-sequence galaxies from the SIMBA simulations, with line emission modeled by the Simulator of Galaxy Millimeter/Submillimeter Emission. Though most (similar to 50%-100%) of the gas mass in our simulations is ionized, the bulk (>50%) of the [C II] emission comes from the molecular phase. We find a sublinear (slope 0.78 +/- 0.01) log L-[C II]-log M-mol relation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies at z similar or equal to 6. We derive a median [C II]-to-M-mol conversion factor of alpha([C )(II]) similar or equal to 18 M-circle dot/L-circle dot. This is lower than the average value of similar or equal to 30 M-circle dot/L-circle dot 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 [C II] observations of low-mass galaxies. For our simulations, [C 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-[C (II)] is more tightly correlated with M-mol than with star formation rate (SFR), and both the log L-[C II] - log M-mol and log L-[C II]-log SFR relations arise from the Kennicutt-Schmidt relation. Our findings suggest that L-[C II] is a promising tracer of the molecular gas at the earliest cosmic epochs.

AB - We investigate the fine-structure [C II] line at 158 mu m as a molecular gas tracer by analyzing the relationship between molecular gas mass (M-mol) and [C II] line luminosity (L-[C (II)]) in 11,125 z similar or equal to 6 star-forming, main-sequence galaxies from the SIMBA simulations, with line emission modeled by the Simulator of Galaxy Millimeter/Submillimeter Emission. Though most (similar to 50%-100%) of the gas mass in our simulations is ionized, the bulk (>50%) of the [C II] emission comes from the molecular phase. We find a sublinear (slope 0.78 +/- 0.01) log L-[C II]-log M-mol relation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies at z similar or equal to 6. We derive a median [C II]-to-M-mol conversion factor of alpha([C )(II]) similar or equal to 18 M-circle dot/L-circle dot. This is lower than the average value of similar or equal to 30 M-circle dot/L-circle dot 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 [C II] observations of low-mass galaxies. For our simulations, [C 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-[C (II)] is more tightly correlated with M-mol than with star formation rate (SFR), and both the log L-[C II] - log M-mol and log L-[C II]-log SFR relations arise from the Kennicutt-Schmidt relation. Our findings suggest that L-[C II] is a promising tracer of the molecular gas at the earliest cosmic epochs.

KW - STAR-FORMING GALAXIES

KW - CO-TO-H-2 CONVERSION FACTOR

KW - SUBMILLIMETER GALAXIES

KW - INTERSTELLAR-MEDIUM

KW - ATOMIC CARBON

KW - EMISSION

KW - ACCURATE

KW - MODEL

KW - EVOLUTION

KW - RELEASE

U2 - 10.3847/1538-4357/ac5cba

DO - 10.3847/1538-4357/ac5cba

M3 - Journal article

VL - 929

JO - Astrophysical Journal

JF - Astrophysical Journal

SN - 0004-637X

IS - 1

M1 - 92

ER -