Compact steep-spectrum and peaked-spectrum radio sources

Abstract

Compact steep-spectrum (CSS) and peaked spectrum (PS) radio sources are compact, powerful radio sources. The multi-frequency observational properties and current theories are reviewed with emphasis on developments since the earlier review of O'Dea (1998). There are three main hypotheses for the nature of PS and CSS sources. (1) The PS sources might be very young radio galaxies which will evolve into CSS sources on their way to becoming large radio galaxies. (2) The PS and CSS sources might be compact because they are confined (and enhanced in radio power) by interaction with dense gas in their environments. (3) Alternately, the PS sources might be transient or intermittent sources. Each of these hypotheses may apply to individual objects. The relative number in each population will have significant implications for the radio galaxy paradigm. Proper motion studies over long time baselines have helped determine hotspot speeds for over three dozen sources and establish that these are young objects. Multifrequency polarization observations have demonstrated that many CSS/PS sources are embedded in a dense interstellar medium and vigorously interacting with it. The detection of emission line gas aligned with the radio source, and blue-shifted HI absorption and [OIII] emission lines indicates that AGN feedback is present in these objects -possibly driven by the radio source. CSS/PS sources with evidence of episodic AGN over a large range of time-scales have been discussed. The review closes with a discussion of open questions and prospects for the future.

Morphological transition of the compact radio lobe in 3C84 via the strong jet-cloud collision

“…The evolution model where compact radio lobes expand and become large FR Is and FR IIs are well consistent with radio observational data (e.g., Kawakatu et al 2008;Kunert-Bajraszewska et al 2010;O'Dea & Saikia 2020). Kawakatu et al (2008) studied the properties of more than 100 radio lobes and by comparing the hot spot advancing speed with the sound speed of the ambient medium, they indicated that only compact symmetric objects whose initial advance speed is faster than about 0.1 c can evolve into FR II class.…”

Radio Spectra of Luminous, Heavily Obscured WISE-NVSS Selected Quasars

“…The radio characteristics of many sources are consistent with powerful (26.8 < log(L 1.4 GHz /W Hz −1 ) < 28), sub-galactic, and high pressure (log(P 10 GHz /dyne cm −3 ) > −7) radio sources typical of those seen in compact and young radio AGN (e.g., Readhead et al 1996;Orienti & Dallacasa 2014). The radio sources in our sample are therefore similar to other well-known classes of young and compact radio sources: the Compact Steep Spectrum (CSS) sources, Gigahertz-Peaked Spectrum (GPS) sources, and High-Frequency Peakers (HFP) (see reviews by O'Dea 1998;O'Dea & Saikia 2020).…”

“…Furthermore, it can explain the global properties of the GPS/CSS population, e.g., the observed linear size vs. turnover relation (O'Dea & Baum 1997) and provides magnetic field estimates consistent with the equipartition fields estimated from the optically thin part of the spectrum (Orienti & Dallacasa 2008a). The consensus, then, is that SSA will always be present to some degree in radio-emitting plasma (Fanti 2009;Orienti 2016;O'Dea & Saikia 2020). In what follows we continue to assume that the peaked spectra result from SSA.…”

Jet-induced feedback in the [O III] lines of early evolution stage active galactic nuclei

“…The relativistic jets of NLS1s are usually rather compact (Gu et al 2015;Berton 2018;Liao & Gu 2020;Chen et al 2020), although some exceptions are known (e.g., Gliozzi et al 2010;Richards & Lister 2015;Congiu et al 2017a;Rakshit et al 2018;Gabányi et al 2018;Congiu et al 2020). This has led some authors to suggest that NLS1s may be connected with classes of young radio galaxies such as compact steep-spectrum (CSS) sources and gigahertz-peaked sources (GPS) (Oshlack et al 2001;Gallo 2006;Komossa et al 2008;Caccianiga et al 2014;Berton et al 2017;Caccianiga et al 2017;Liao & Gu 2020;O'Dea & Saikia 2020;Yao & Komossa 2020). Indeed, several radio galaxies show signs of line shifts and broadening induced by the presence of jets (Tadhunter et al 2001;Marziani et al 2003;Holt et al 2006;Venturi et al 2020), and this seems particularly common in young radio galaxies, where the jet is directly interacting with the ISM (Morganti et al 2015;Orienti 2016).…”