On the evolution of young radio-loud AGN

Abstract

This paper describes an investigation of the early evolution of extragalactic radio sources using samples of faint and bright Gigahertz Peaked Spectrum (GPS) and Compact Steep Spectrum (CSS) radio galaxies. Correlations found between their peak frequency, peak flux density and angular size provide strong evidence that synchrotron self absorption is the cause of the spectral turnovers, and indicate that young radio sources evolve in a self-similar way. In addition, the data seem to suggest that the sources are in equipartition while they evolve. If GPS sources evolve to large size radio sources, their redshift dependent birth-functions should be the same. Therefore, since the lifetimes of radio sources are thought to be short compared to the Hubble time, the observed difference in redshift distribution between GPS and large size sources must be due to a difference in slope of their luminosity functions. We argue that this slope is strongly affected by the luminosity evolution of the individual sources. A scenario for the luminosity evolution is proposed in which GPS sources increase in luminosity and large scale radio sources decrease in luminosity with time. This evolution scenario is expected for a ram-pressure confined radio source in a surrounding medium with a King profile density. In the inner parts of the King profile, the density of the medium is constant and the radio source builds up its luminosity, but after it grows large enough the density of th e surrounding medium declines and the luminosity of the radio source decreases. A comparison of the local luminosity function (LLF) of GPS galaxies with that of extended sources is a good test for this evolution scenario [abridged].Comment: LaTeX, 11 pages, 8 figures; Accepted by MNRAS. Related papers may be found at http://www.ast.cam.ac.uk/~snellen . Valuable comments of referee incorporated. More discussion on simulation

Radio-ExcessIRASGalaxies. II. Host Galaxies

“…Thus, objects should evolve to lower radio power. However, it has been shown that very young compact radio sources will undergo a phase in which they increase in luminosity as they expand, because of the approximately constant density of the surrounding medium (Snellen et al 2000). GPS sources have similar optical luminosities to the FIR-luminous radio-excess galaxies (O'Dea et al 1996), but are much more powerful radio sources, placing them well into the FR II region of the diagram.…”

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).…”

Multifrequency VLBA observations of two compact symmetric objects

“…As presented by Snellen et al, (2000) it is possible to set limits on the luminosity evolution of radio sources by exploiting the radio power -linear size (P-D) diagram as shown in Fig.2.8 (Snellen et al, 2000a).…”