|19th of March 2018|
|High-resolution Observations of Low-luminosity Sources|
Using high angular-resolution observations with the Long Baseline
Array, Collier et al. have detected six low luminosity objects
thought to be young radio galaxies. Referred to as
Gigahertz-Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS)
sources, these objects represent galaxies whose radio emission is very
compact and which reach a peak brightness between a
few hundred MHz and ~1 GHz. Using measurements from a range of
radio telescopes, including the
Australian Square Kilometer Array Pathfinder (ASKAP), Collier et
al. determined the sizes and radio spectra of these objects, comparing
them to the well known population of high-luminosity GPS and CSS
sources, and finding them to be similar in spectral shape and peak
frequency, size and age.
The image to the left shows one of the objects (CI0008) resolved into two components, extending over 450 milli-arcseconds (i.e. an angle of 0.000125 degrees on the sky), which, at a distance about 3 billion light years, corresponds to a projected size of only 6000 light years across, which is very small for a radio galaxy. These components are most likely the lobes or hotspots of the galaxy, a region where the matter ejected from the near the central supermassive black hole collides with the surrounding dense medium. The image to the right shows the models fit to measurements of the radio spectrum of CI0008. The green power law model, which is followed by the majority of other radio sources, fits poorly to the spectrum. The blue and orange models fit well to the spectrum, representing scenarios in which the low frequency emission is absorbed, or the high frequency emission is depleted, respectively.
The paper will soon appear in the Monthly Notices of the Royal Astronomical Society, with a preprint available here.