Radio and Submillimetre Observation

Radio and submillimetre observation detects the longest-wavelength cosmic radiation using single dishes and interferometric arrays, probing cold gas, magnetic fields, and non-thermal emission.

Definition

Radio and submillimetre observation is the detection and imaging of celestial radiation at wavelengths from roughly a millimetre to many metres, using antennas and, frequently, interferometric arrays to attain high resolution.

Scope

This topic covers observation at radio and submillimetre wavelengths, including single-dish telescopes, heterodyne and bolometric receivers, and the interferometry and aperture synthesis that combine many antennas to achieve high angular resolution. It addresses the physical processes accessible in this regime, such as synchrotron emission, thermal dust emission, and spectral-line transitions of atoms and molecules.

Core questions

• How do interferometry and aperture synthesis achieve high angular resolution from arrays of antennas?
• What emission processes dominate at radio and submillimetre wavelengths?
• How are spectral lines such as the 21-cm line and molecular transitions observed and interpreted?
• What distinguishes heterodyne from continuum detection in this regime?

Key theories

Aperture synthesis interferometry

Combining signals from pairs of antennas samples the spatial structure of a source, and many baselines together synthesize an image with the resolution of a telescope as large as the array's extent.

Synchrotron and thermal emission

Radio continuum arises largely from synchrotron radiation of relativistic electrons in magnetic fields, while the submillimetre is dominated by thermal emission from cold dust.

Clinical relevance

Radio and submillimetre data reveal cold molecular clouds and star formation, neutral hydrogen tracing galaxy dynamics, pulsars and active galactic nuclei, and the cosmic microwave background, complementing what shorter wavelengths can show.

History

Jansky's 1932 detection of Galactic radio emission founded radio astronomy; the subsequent development of aperture-synthesis interferometry by Ryle and others, and later millimetre and submillimetre arrays, brought high-resolution imaging across this regime.

Seminal works

• thompson2017
• wilson2013
• lena2012

Frequently asked questions

Why do radio telescopes need to be so large or use arrays?

Angular resolution depends on the ratio of wavelength to aperture; because radio wavelengths are long, very large dishes or arrays of antennas spread over kilometres are needed to resolve fine detail.

What is the 21-cm line?

It is a radio spectral line emitted by neutral hydrogen at 21 centimetres wavelength, widely used to map the distribution and motion of hydrogen gas in galaxies.