Accretion Disk Model of Short-Timescale Intermittent Activity in Young Radio Sources

Abstract

We associate the existence of short-lived compact radio sources with the intermittent activity of the central engine caused by a radiation pressure instability within an accretion disk. Such objects may constitute a numerous sub-class of Giga-Hertz Peaked Spectrum sources, in accordance with the population studies of radio-loud active galaxies, as well as detailed investigations of their radio morphologies. We perform the model computations assuming the viscosity parametrization as proportional to a geometrical mean of the total and gas pressure. The implied timescales are consistent with the observed ages of the sources. The duration of an active phase for a moderate accretion rate is short enough (< 10 3 − 10 4 years) that the ejecta are confined within the host galaxy and thus these sources cannot evolve into large size radio galaxies unless they are close to the Eddington limit.

Observational Evidence for Young Radio Galaxies Is Triggered by Accretion Disk Instability

“…The relation between ages and bolometric luminosities for young radio galaxies is presented in Figure 2, where the bolometric luminosities of CSS sources calculated from [O iii] luminosities are marked with extra open squares. We find that the ages are positively correlated with the bolometric luminosities in these young radio galaxies, which is consistent with the prediction of radiation pressure instability in accretion disks (Czerny et al 2009). We plot the dashed lines corresponding to Equation (1) with viscosity parameters α = 10 −4 and 1 in Figure 2.…”

“…We then compare the ages of young radio sources with the half of the outburst durations in the BH mass-accretion rate (in Eddington unit, M BH -ṁ) plane where the outbursts are assumed to be triggered by the radiation pressure instabilities of accretion disks. To do so, we convert the contour map of α = 0.2 in Czerny et al (2009, Figure 5) to the case of T burst /2 with α = 0.1 using the scaling relation of Equation (1), since we find that most of the young radio sources can, on the average, be described by α 0.1 in the L bol -age relation. The ages of young radio sources are divided into four bins as Figure 3.…”

“…In this Letter, we estimate the bolometric luminosities and BH masses for a sample of young radio galaxies with known ages. We then test whether the ages of young radio galaxies are consistent with the durations of outbursts or not, where the outbursts are assumed to be triggered by the radiation pressure instabilities of accretion disks (e.g., Czerny et al 2009). Throughout this paper, we assume the following cosmology: H 0 = 70 km s −1 Mpc −1 , Ω 0 = 0.3, and Ω Λ = 0.7.…”

Evidence of a double-double morphology in B 0818+214

“…ionisation instability operating on longer timescales (Hatziminaoglou et al 2001;Janiuk et al 2004, and references therein). On the other hand, in the most recent activity cycle, the central source is intermittent due to radiation-pressure instability operating on much shorter timescales (Czerny et al 2009). Hence, it appears that two accretion disk instability mechanisms, ionisation and radiationpressure driven, could be at work in the same galaxy and the outburst resulting from the short-timescale instability may occur during the quiescent phase of the long-timescale instability.…”

Multifrequency VLBA observations of two compact symmetric objects

“…This may be interpreted considering that the di↵erent orientation between the di↵use radio emission and the new radio structure may be connected with merger events (Czerny et al, 2009). This results in the renewing activity of the central engine accompanied by the re-orientation of the jet axis.…”