We investigate the fine-structure [C
- Award ID(s):
- 1715206
- NSF-PAR ID:
- 10077055
- Date Published:
- Journal Name:
- Astrophysical journal
- ISSN:
- 1538-4357
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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Abstract ii ] line at 158μ m as a molecular gas tracer by analyzing the relationship between molecular gas mass (M mol) and [Cii ] line luminosity (L [CII ]) in 11,125z ≃ 6 star-forming, main-sequence galaxies from thesimba simulations, 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) relation, in contrast with the linear relation derived from observational samples of more massive, metal-rich galaxies atz ≲ 6. We derive a median [Cii ]-to-M molconversion factor ofα [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 COJ = 1–0, especially at the lowest metallicities, where much of the gas isCO-dark . We find thatL [CII ]is more tightly correlated withM molthan with star formation rate (SFR), and both the and relations arise from the Kennicutt–Schmidt relation. Our findings suggest thatL [CII ]is a promising tracer of the molecular gas at the earliest cosmic epochs. -
Abstract Observations of local star-forming galaxies (SFGs) show a tight correlation between their singly ionized carbon line luminosity ($L_{\rm [C\, \small {II}]}$) and star formation rate (SFR), suggesting that $L_{\rm [C\, \small {II}]}$ may be a useful SFR tracer for galaxies. Some other galaxy populations, however, are found to have lower $L_{\rm [C\, \small {II}]}{}/{}\rm SFR$ than local SFGs, including the infrared-luminous, starburst galaxies at low and high redshifts as well as some moderately star-forming galaxies at the epoch of re-ionization (EoR). The origins of this ‘$\rm [C\, \small {II}]$ deficit’ is unclear. In this work, we study the $L_{\rm [C\, \small {II}]}$-SFR relation of galaxies using a sample of z = 0 − 8 galaxies with M* ≈ 107 − 5 × 1011 M⊙ extracted from cosmological volume and zoom-in simulations from the Feedback in Realistic Environments (fire) project. We find a simple analytic expression for $L_{\rm [C\, \small {II}]}$/SFR of galaxies in terms of the following parameters: mass fraction of $\rm [C\, \small {II}]$-emitting gas ($f_{\rm [C\, \small {II}]}$), gas metallicity (Zgas), gas density (ngas) and gas depletion time ($t_{\rm dep}{}={}M_{\rm gas}{}/{}\rm SFR$). We find two distinct physical regimes: $\rm H_2$-rich galaxies where tdep is the main driver of the $\rm [C\, \small {II}]$ deficit and $\rm H_2$-poor galaxies where Zgas is the main driver. The observed $\rm [C\, \small {II}]$ deficit of IR-luminous galaxies and early EoR galaxies, corresponding to the two different regimes, is due to short gas depletion time and low gas metallicity, respectively. Our result indicates that the $\rm [C\, \small {II}]$ deficit is a common phenomenon of galaxies, and caution needs to be taken when applying a constant $L_{\rm [C\, \small {II}]}$-to-SFR conversion factor derived from local SFGs to estimate cosmic SFR density at high redshifts and interpret data from upcoming $\rm [C\, \small {II}]$ line intensity mapping experiments.
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Characterizing the physical conditions (density, temperature, ionization state, metallicity, etc) of the interstellar medium is critical to improving our understanding of the formation and evolution of galaxies. In this work, we present a multi-line study of the interstellar medium in the host galaxy of a quasar at
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Abstract We present a Keck/MOSFIRE rest-optical composite spectrum of 16 typical gravitationally lensed star-forming dwarf galaxies at 1.7 ≲
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null (Ed.)ABSTRACT We present results of MUSE-ALMA haloes, an ongoing study of the circumgalactic medium (CGM) of galaxies (z ≤ 1.4). Using multiphase observations we probe the neutral, ionized, and molecular gas in a subsample containing six absorbers and nine associated galaxies in the redshift range z ∼ 0.3–0.75. Here, we give an in-depth analysis of the newly CO-detected galaxy Q2131−G1 (z = 0.42974), while providing stringent mass and depletion time limits for the non-detected galaxies. Q2131−G1 is associated with an absorber with column densities of log(NH i/cm−2) ∼ 19.5 and $\textrm {log}(N_{\textrm {H}_2}/\textrm {cm}^{-2}) \sim 16.5$, and has a star formation rate of SFR = 2.00 ± 0.20 M⊙yr−1, a dark matter fraction of fDM(r1/2) = 0.24–0.54, and a molecular gas mass of $M_\textrm {mol} = 3.52 ^{+3.95}_{-0.31} \times 10^9 \,\, \textrm {M}_{\odot }$ resulting in a depletion time of τdep < 4.15 Gyr. Kinematic modelling of both the CO (3–2) and [O iii] λ5008 emission lines of Q2131−G1 shows that the molecular and ionized gas phases are well aligned directionally and that the maximum rotation velocities closely match. These two gas phases within the disc are strongly coupled. The metallicity, kinematics, and orientation of the atomic and molecular gas traced by a two-component absorption feature are consistent with being part of the extended rotating disc with a well-separated additional component associated with infalling gas. Compared to emission-selected samples, we find that H i-selected galaxies have high molecular gas masses given their low star formation rate. We consequently derive high depletion times for these objects.more » « less