The Compact Steep‐Spectrum and Gigahertz Peaked‐Spectrum Radio Sources

Abstract

I review the radio to X-ray properties of gigahertz peaked-spectrum (GPS) and compact steepspectrum (CSS) sources, the current hypotheses for their origin, and their use to constrain the evolution of powerful radio galaxies. The GPS and CSS sources are compact, powerful radio sources with well-defined peaks in their radio spectra (near 1 GHz in the GPS and near 100 MHz in the CSS). The GPS sources are entirely contained within the extent of the narrow-line region (Շ1 kpc), while the CSS sources are contained entirely within the host galaxy (Շ15 kpc). The peaks in the spectra are probably due to synchrotron self-absorption, though free-free absorption through an inhomogeneous screen may also play a role. The turnover frequency varies with linear size l as , suggesting a simple physical relationship between these parameters. The radion ∝ l m morphologies are strikingly like those of the large-scale classical doubles, though some sources can have very distorted morphologies suggestive of interactions. Radio polarization tends to be low, and in some cases the Faraday rotation measures can be extremely large. The IR properties are consistent with stellar populations and active galactic nucleus (AGN) bolometric luminosity similar to that of the 3CR classical doubles. The optical host galaxy properties (absolute magnitude, Hubble diagram, evidence for interaction) are consistent with those of the 3CR classical doubles. CSS sources at all redshifts exhibit high surface brightness optical light (most likely emission-line gas) that is aligned with the radio axis. The optical emission-line properties suggest (1) interaction of the radio source with the emission-line gas and (2) the presence of dust toward the emission-line regions. Xray observations of high-redshift GPS quasars and a couple of GPS galaxies suggest the presence of significant columns of gas toward the nuclei. Searches for cold gas in the host galaxies have revealed large amounts of molecular gas and smaller amounts of atomic gas in several sources, though probably not enough to confine the radio sources. The main competing models for the GPS and CSS sources are that (1) they are frustrated by interaction with dense gas in their environments and (2) they are young and evolving radio sources that will become large-scale sources. Combining the bright GPS and CSS samples with the 3CR results in a sample spanning a range in source size of 10 5 that can be used to study source evolution. The number density versus linear size relation is consistent with a picture in which the sources expand with constant velocity and the radio power drops with linear size l according to . This strong evolution suggests that at least some of the Ϫ0.5 P ∝ l GPS and CSS sources evolve to become lower luminosity FR 1 radio sources. The GPS and CSS sources are important probes of their host galaxies and will provide critical clues to the origin and evolution of powerful radio sources. 1 ergs s Ϫ1 cm Ϫ2 Hz Ϫ1 . Ϫ23 1 Jy ϭ 10 2 We define spectral index a such that .

High-resolution images of five radio quasars at early cosmological epochs

“…The rest-frame 5-GHz luminosities of the main components of our sources (L ∼ 10 26 −10 27 W Hz −1 ; Table 5) are comparable to the values of a large sample of gigahertz peaked-spectrum (GPS) and compact steep-spectrum (CSS) sources compiled by O'Dea (1998). Our values refer to the VLBI components and can therefore be regarded as lower limits to the radio luminosities of the whole sources.…”

The X-ray view of giga-hertz peaked spectrum radio galaxies

“…GPS sources are characterised by a simple convex radio spectrum peaking near 1 GHz Lister 2003;O'Dea 1998). They represent about 10% of the 5-GHz selected sources.…”

Radio spectra of bright compact sources at z>4.5

“…The observed turnover (or peak) frequencies (νo) of the CSS, MPS, GPS and HFP sources are νo < 0.5 GHz, νo < 1 GHz, 1 < νo < 5 GHz and νo > 5 GHz (O'Dea 1998;Dallacasa et al 2000;Coppejans et al 2015), respectively. These sources are believed to be young (rather than confined) AGN, some of which will likely evolve into FR I and FR II radio galaxies (Begelman 1996;O'Dea 1998;Snellen et al 2000;Conway 2002; De Vries et al 2002;Murgia et al 2002;Murgia 2003;Fanti 2009;An & Baan 2012;Orienti 2016). For the nearby (z ∼ 1) CSS, MPS, GPS and HFP sources, an empirical relation exists between the rest-frame turnover frequencies (νr, where νr = νo(1 + z)) and the linear sizes of the sources (O'Dea 1998; Snellen et al 2000;Orienti & Dallacasa 2014).…”