Volume 645, January 2021
|Number of page(s)||18|
|Section||Cosmology (including clusters of galaxies)|
|Published online||26 January 2021|
Diagnosing the interstellar medium of galaxies with far-infrared emission lines
I. The [C II] 158 μm line at z ∼ 0
Kapteyn Astronomical Institute, University of Groningen, Landleven 12, 9747 AD Groningen, The Netherlands
2 SRON Netherlands Institute for Space Research, Landleven 12, 9747 AD Groningen, The Netherlands
3 Lorentz Institute for Theoretical Physics, Leiden University, 2333 CA Leiden, The Netherlands
Accepted: 24 November 2020
Context. 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 μm is an important observable as it provides constraints on the interstellar medium (ISM) cooling processes.
Aims. 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 μm line emission in the local Universe.
Methods. 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.
Results. 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 L[C II–star formation rate (SFR) relation in the local Universe within 0.4 dex scatter.
Conclusions. 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 SFR ∼ 0.01–1 M⊙ yr−1, but the ionised phase dominates at lower SFRs. Galaxies above solar metallicity exhibit lower L[C II/SFR ratios for the neutral phase. In comparison, the L[C II/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 L[C II deficit at high infrared luminosities, although EAGLE simulations do not reach these luminosities at z = 0.
Key words: ISM: lines and bands / Galaxy: formation / Galaxy: evolution / ISM: clouds / evolution / methods: numerical
© ESO 2021
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