Far-Infrared Emission and Star Formation in Galaxies

Far-infrared (FIR) emission provides a window into the cold and dusty interstellar medium where stars are born. Dust grains absorb ultraviolet and optical photons from young, massive stars and re-emit that energy as thermal radiation in the 30–300 µm range. Key cooling lines, notably the 158 µm fine-structure transition of ionised carbon ([C II]), and rotational transitions of molecules such as CO, trace distinct phases of the interstellar medium. The brightness of these tracers correlates with the rate at which galaxies convert gas into stars, yielding empirical calibrations for the star formation rate (SFR). Surveys with space observatories have revealed that in low-metallicity environments a large fraction of molecular hydrogen is “CO-dark” yet detectable via [C II] emission, while in dense starbursts the far-infrared line-to-continuum ratios can decline due to strong radiation fields and dust heating. By combining spectral line measurements, far-IR photometry and modelling of photodissociation regions, researchers can reconstruct the physical conditions—density, temperature and radiation intensity—that govern star formation on scales from individual clouds to entire galaxies. This work is essential for understanding galaxy evolution across cosmic time and for interpreting observations of the distant Universe with next-generation facilities.

Research from Nature Portfolio

No recent Nature Portfolio content available.

Far-Infrared Emission and Star Formation in Galaxies publication trend

The graph below shows the total number of articles in far-infrared emission and star formation in galaxies across all publications each year (not limited to Nature Index journals).

Technical terms

Far-infrared emission: Thermal radiation from dust grains at wavelengths of roughly 30–300 µm, produced by absorption of ultraviolet and optical photons from young stars.

[C II] 158 µm line: A fine-structure transition of singly ionised carbon that is one of the brightest cooling lines of the neutral interstellar medium and a tracer of photodissociation regions.

Photodissociation region (PDR): The interface layer in the interstellar medium where far-ultraviolet photons dissociate molecules and heat gas, producing characteristic line and continuum emission.

CO-dark molecular gas: Molecular hydrogen that is not traced by carbon monoxide emission, often prevalent in low-metallicity or strongly irradiated environments and instead detected via atomic carbon or ionised carbon lines.

CO-to-H₂ conversion factor (αCO): The proportionality constant used to convert observed CO line luminosity into a molecular hydrogen mass estimate, which depends on metallicity, density and cloud structure.

References

1. Modeling the molecular gas content and CO-to-H2 conversion factors in low-metallicity star-forming dwarf galaxies. Astronomy & Astrophysics (2023).
2. Shock Enhanced [C ii] Emission from the Infalling Galaxy Arp 25 ∗ ∗ Data obtained with FIFI-LS and HAWC+ on board SOFIA.. The Astrophysical Journal (2023).
3. Tracing the total molecular gas in galaxies: [CII] and the CO-dark gas⋆. Astronomy & Astrophysics (2020).