Diagnosing the interstellar medium of galaxies with far-infrared emission lines I. The [C II] 158 microns line at z~0

Abstract

Atomic fine structure lines have been detected in the local Universe and at high redshifts over the past decades. The [C II] emission line at 158 $\mu$m is an important observable as it provides constraints on the interstellar medium (ISM) cooling processes. We develop a physically motivated framework to simulate the production of far-infrared line emission from galaxies in a cosmological context. This first paper sets out our methodology and describes its first application, simulating the [C II] 158 $\mu$m line emission in the local Universe. We combine the output from EAGLE cosmological hydrodynamical simulations with a multi-phase model of the ISM. Gas particles are divided into three phases: dense molecular gas, neutral atomic gas and diffuse ionised gas (DIG). We estimate the [C II] line emission from the three phases using a set of Cloudy cooling tables. Our results agree with previous findings regarding the contribution of these three ISM phases to the [C II] emission. Our model shows good agreement with the observed ${\mathrm{L}}_{[\mathrm{CII}]}$-star formation rate (SFR) relation in the local Universe within 0.4 dex scatter. The fractional contribution to the [C II] line from different ISM phases depends on the total SFR and metallicity. The neutral gas phase dominates the [C II] emission in galaxies with $\mathrm{SFR}\sim 0.01$-$1{\mathrm{M}}_{\odot }\mathrm{y}{\mathrm{r}}^{-1}$, but the ionised phase dominates at lower SFRs. Galaxies above solar metallicity exhibit lower ${\mathrm{L}}_{[\mathrm{CII}]}$/SFR ratios for the neutral phase. In comparison, the ${\mathrm{L}}_{[\mathrm{CII}]}$/SFR ratio in the DIG is stable when metallicity varies. We suggest that the reduced size of the neutral clouds, caused by increased SFRs, is the likely cause for the ${\mathrm{L}}_{[\mathrm{CII}]}$ deficit at high infrared luminosities, although EAGLE simulations do not reach these luminosities at $z=0$.

Accepted for publication in A&A; 16 pages, 11 figures, 4 tables (plus appendix)

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Cited by in corpus (7)

• Regular rotation and low turbulence in a diverse sample of z ~ 4.5 galaxies observed with ALMA
• Inferring the HII region escape fraction of ionizing photons from infrared emission lines in metal-poor star-forming dwarf galaxies
• Atomic and molecular gas as traced by [C II] emission
• Diagnosing the interstellar medium of galaxies with far-infrared emission lines II. [C II], [O I], [O III], [N II] and [N III] up to z=6
• CII*/CII ratio in high-redshift DLAs: ISM phase separation drives the observed bimodality of [CII] cooling rates
• Tight correlation of star formation with [Ci] and CO lines across cosmic time
• Measuring the HI content of individual galaxies out to the epoch of reionization with [CII]