GPS/CSS radio sources and their relation to other AGN

Abstract

AbstractWe are entering a new era of sensitive, large‐area and multi‐frequency radio surveys that will allow us to identify Gigahertz‐Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio sources over a wide range in radio luminosity and study them within the context of the overall radio‐source populations to which they belong. “Classical” GPS/CSS objects are extremely luminous radio sources with a compact double morphology, commonly thought to represent the earliest stages in the life cycle of powerful radio galaxies (e.g. O'Dea 1998). It is now becoming easier to identify GPS/CSS candidates with much lower radio luminosity – particularly in the nearby Universe. These less powerful objects, with typical 1.4 GHz radio luminosities of 1023 to 1025 W Hz–1, include peaked‐spectrum radio sources with a core‐jet morphology on parsec scales as well as high‐frequency GPS‐like peaked components embedded within lower‐frequency extended emission. In the latter case, the presence of a young GPS component may not be evident from low‐frequency data alone. Many radio galaxies in the local Universe have a compact (FR‐0) morphology, and appear to lack extended radio emission on kiloparsec scales. The relationship of these FR‐0 objects to the classical GPS/CSS radio sources remains unclear – some of them may represent short‐lived episodes of AGN activity that will not lead to an extended FR‐1 or FR‐2 radio galaxy. Future wide‐band radio surveys will shed more light on this – such surveys should ideally be coordinated to cover the full frequency range from 100 MHz to 100 GHz in order to sample all stages of GPS/CSS evolution in an unbiased way. (© 2016 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)