Young radio sources and the duty-cycle of the radio emission M. Orienti INAF-IRA Bologna Collaborators: D. Dallacasa, M. Murgia, F. D'Ammando, M. Giroletti, G. Giovannini
Open questions Duty-cycle of the radio emission - how many on/off phases? - how long do they last? The influence of the ambient medium Fraction of radio sources
Compact radio sources P1.4 GHz > 1025 W/Hz LS < 1 20 kpc peak~100 MHz - few GHz 500 pc Scaled down version of the large classical radio galaxies High fraction (~10%-30%) in flux-limited sample 240 kpc
The evolutionary scenario Compact Young Radiative ages Kinematic ages 103 105 yr Compact Frustrated No evidence of particularly dense medium able to frustrate the radio emission for the entire lifetime Fanti 00, Siemiginowska 05 Murgia 03
The evolutionary scenario Compact Young Radiative ages Kinematic ages 103 105 yr Compact Frustrated No evidence of particularly dense medium able to frustrate the radio emission for the entire lifetime, BUT... Fanti 00, Siemiginowska 05 Murgia 03
Fading radio sources? The number of young radio sources in flux-density-limited sample is too high if compared with what is expected in evolutionary models Luminosity evolution Fading objects Gugliucci+ 05 Snellen+ 00 Luminosity decreases as the source grows The source age peaks at ~500 yr
PKS 1518+037: a study case
A young but dying object? CI: Bad fit and very steep spectral energy distribution No core detection Compact components have steep spectral index α = 1.1 δ = 3.2 CI OFF: Standard values. Only electrons with low energies are present Lack of active regions δ = 2.4 α = 0.7 νb = 830 MHz Heq = 4 mg trad = 2700±600 yr toff/tr = 0.2 1 kpc Orienti+10 γ = 400-600
Fossils from a recent past On kpc scales: J0111+3906: 128 kpc trelic ~ 107 108 yr 60 pc Tinti+05 On pc-scales: 7 pc J1511+0518: 50 pc OQ208: 43 pc trelic ~ 103 104 yr Orienti & Dallacasa 08 10 pc Luo+07
The duty-cycle of the radio emission CSO Restarted Tinti+05 FRI/II Relic Murgia+11 Low frequency observations can pick up the radio emission from the lowest energy tail of the electron populations. High angular resolution at low frequency is necessary to detect remnant from previous radio activity around young radio sources to find how many and how long the various phases may last
Searching for fading young sources To determine the incidence of short-lived objects we selected a sub-sample of candidate fading objects from the B3-VLA CSS sample by Fanti et al. (2001). The B3-VLA CSS sample is made of sources with linear sizes (i.e. ages) from 100 pc (103 yr) to 15 kpc (105 yr). The selection criteria are: Steep optically-thin spectrum with >1.0 No evidence of active regions (i.e. core, HS) We ended up with a sample of 18 objects. 9 sources with LS < 1 kpc 9 sources with LS > 1 kpc Smaller sources: new multi-frequency VLBA observations obtained Larger sources: archival multi-frequency VLA data have been retived
The large sources B1350+432 Double radio source LS = 6.5 kpc Fanti+01 Spectral analysis: CI OFF single ejection model νb < 800 MHz Steep spectral index across the entire source Rossetti+06 trad ~ 105 yr
The small sources B1133+432 Double radio source Steep spectral index across the entire source No optical counterpart α = 0.95 LAS: 35 mas νb < 1.4 GHz LS: 150 pc @ z=1 No clear evidence of active regions trad ~ a few 103 yr
The small sources B1049+384 Orienti+, in prep. Complex structure LS ~ 900 pc α > 1.0 The new VLBA observations at 8.4 GHz pointed out the source core with a flat spectral index and a hint of the jet. The source has been removed from the sample
The role of the ambient medium The interaction between the jet and the ambient medium may influence the source growth Temporary frustrating the jet expansion, decreasing adiabatic losses and increasing synchrotron losses Orienti+ 2007; Dallacasa+ 2013 Asymmetric luminosity and arm-length Morganti+ 2004
The role of the ambient medium Compact young radio sources are more asymmetric than classical extended FRII galaxies High fraction (~52%) of objects where the brighter lobe is the closer to the core It may partly explain the excess of compact objects in flux-limited samples Orienti+ 2007 Dallacasa+ 2013
Open questions Duty-cycle of the radio emission - how many on/off phases? One?/More? - how long do they last? It depends The influence of the ambient medium It may strongly influence the radio source evolution Fraction of radio sources Are there any intruders?