Dust Attenuation and Star Formation in Galaxies
Summary
Interstellar dust grains, composed of silicates, carbonaceous compounds and metallic oxides, absorb and scatter ultraviolet and optical photons emitted by young stars, imprinting a characteristic reddening and dimming on galactic spectra. Correcting for this attenuation is essential to recover intrinsic star formation rates and to trace the build-up of stellar mass across cosmic time. Dust attenuation laws, which describe the wavelength dependence of this dimming, vary with grain composition, size distribution and spatial configuration relative to the stellar population. In starburst galaxies, a greyer attenuation curve often applies, while quiescent or low-metallicity systems can exhibit steeper, Small Magellanic Cloud–like behaviour. Observational diagnostics include the Balmer decrement (the ratio of Hα to Hβ emission), the ultraviolet-continuum slope (β) and the infrared excess (IRX, the ratio of infrared to ultraviolet luminosity). Together, these probes address the interplay between dust formation in evolved stars and supernovae, grain growth in the interstellar medium, and the efficiency of conversion of gas into new stars. The global star formation history, derived from multiwavelength surveys, relies on consistent dust corrections to reconcile ultraviolet and infrared estimates, revealing that obscured star formation dominates at low redshift and in massive systems, while unobscured, blue galaxies prevail at early epochs and low masses.
Research from Nature Portfolio
Recent observations extended the detection of a prominent 2,175 Å carbonaceous dust feature to galaxies within the first billion years of cosmic time, implying a rapid formation of small carbonaceous grains in supernova ejecta or Wolf–Rayet winds. This study combined deep near-infrared spectroscopy with models of dust production pathways to demonstrate the early emergence of a Milky Way–like attenuation signature, challenging previous expectations that dust formation would be too slow at very low metallicity. The results demand revisions to theoretical models of dust growth, favouring accelerated grain coagulation in the interstellar medium and efficient seeding by massive star outflows.
Dust Attenuation and Star Formation in Galaxies publication trend
The graph below shows the total number of articles in dust attenuation and star formation in galaxies across all publications each year (not limited to Nature Index journals).
Technical terms
Balmer decrement: The ratio of Hα to Hβ emission-line fluxes, used to infer nebular dust attenuation.
Infrared excess (IRX): The ratio of infrared to ultraviolet luminosity, quantifying the fraction of starlight reprocessed by dust.
Ultraviolet-continuum slope (β): The exponent of the UV spectrum (fλ ∝ λ^β), indicative of dust reddening and intrinsic stellar population age.
Attenuation curve: A function describing how dust attenuation varies with wavelength, shaped by grain properties and geometry.
Polycyclic aromatic hydrocarbons (PAHs): Small carbonaceous molecules that produce distinctive infrared emission features and contribute to the 2175 Å absorption bump.
References
- Carbonaceous dust grains seen in the first billion years of cosmic time. Nature (2023).
- A First Look at Spatially Resolved Balmer Decrements at 1.0. The Astrophysical Journal Letters (2023).
- Dust attenuation law in JWST galaxies at z ∼ 7–8. Astronomy & Astrophysics (2023).
- JWST/NIRSpec Balmer-line Measurements of Star Formation and Dust Attenuation at z ∼ 3–6. The Astrophysical Journal (2023).
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