Extragalactic Radio Source Characteristics and Measurements
Summary
Extragalactic radio sources encompass a diverse population of active galactic nuclei, radio galaxies, quasars and star-forming galaxies beyond the Milky Way. Their emission is dominated by synchrotron radiation from relativistic electrons in magnetic fields, often superimposed on thermal components at higher frequencies. Measurements of flux density across centimetre to submillimetre bands, combined with spectral indices, reveal the energy distributions of particles and magnetic-field strengths. Spectral energy distributions constructed from multiwavelength data probe the relative contributions of accretion-driven jets and star-formation processes. Polarimetric observations yield the degree and orientation of linear polarisation, providing insight into magnetic-field ordering and propagation effects such as Faraday rotation. Advances in interferometry, wide-area surveys and novel analysis techniques have enhanced sensitivity, angular resolution and the ability to characterise variability, morphology and polarisation properties of faint extragalactic sources. These measurements underpin studies of cosmic magnetic fields, galaxy evolution and contamination of cosmic-microwave-background observations.
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Extragalactic Radio Source Characteristics and Measurements publication trend
The graph below shows the total number of articles in extragalactic radio source characteristics and measurements across all publications each year (not limited to Nature Index journals).
Technical terms
Extragalactic radio source: An astronomical object outside the Milky Way that emits strongly in the radio band, typically an active galactic nucleus or star-forming galaxy.
Flux density: The observed power per unit area per unit frequency from a radio source, usually expressed in janskys (Jy).
Spectral index: The exponent α in the power-law relationship Sν ∝ ν^α, describing how flux density S varies with frequency ν.
Polarisation fraction: The ratio of the polarised flux density to the total flux density, indicating the degree of alignment of electromagnetic fields.
Synchrotron emission: Radiation produced by relativistic electrons spiralling in magnetic fields, dominating the radio output of many extragalactic sources.
Spectral energy distribution (SED): A plot of flux density versus frequency over the electromagnetic spectrum, used to infer physical properties of sources.
References
- Infrared Galaxies Detected by the Atacama Cosmology Telescope. The Astrophysical Journal Supplement Series (2023).
- Constraining the polarisation flux density and angle of point sources by training a convolutional neural network. Astronomy & Astrophysics (2023).
- ALMA Band 3 polarimetric follow-up of a complete sample of faint PACO sources. Monthly Notices of the Royal Astronomical Society (2019).
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