1. Large-scale Jets in DRAGNs
J. P. Leahy
Jodrell Bank Observatory,
University of Manchester
(Thanks to NRAO for financial support)
AAS Meeting Wednesday 5th June 2002

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DRAGNs
Radio sources powered by jets from AGN:
Radio Galaxies,
Quasars
Seyfert galaxies etc.
Relativistic (initial) flow speeds:
Lorentz factor  ~ 3-10.
This talk will focus on the more powerful examples, I.e. radio galaxies & quasars.
Yes it’s an acronym.
A. Bridle et al./NRAO
AAS Meeting Wednesday 5th June 2002

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Questions
How are DRAGNs born?
How stable are the jets?
How long do DRAGNs live?
How do they die?
Is there an after-life?
AAS Meeting Wednesday 5th June 2002

4. Activity Power Spectrum
???
Structure
of lobes
Structure
in jets
Direct
Observations
Crude representation: intermittancy, i.e. phase correlated.
Peak around 30 Myr corresponds to overall life time.
Different observational approaches give us different windows on this function.
AAS Meeting Wednesday 5th June 2002

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Switch-on
Smallest DRAGNs have dynamical ages D/v ~ 500 yrs from measured hotspot advance
Owsianik & Conway (1998a,b)
Start-up time ~ 1 Million times shorter than galaxy merger timescale, O(108) yrs
On larger scales we can’t do this: we only see a single instant.
Actually not quite true, as we’ll see.
Like explaining why you are late for work by blaming the transition from barbarian society to civilisation.
(Courtesy G. Taylor)
AAS Meeting Wednesday 5th June 2002

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Pointing Stability
4.6 Mpc
Orientation can be stable for 0(108) yr:
straightness of some Giant DRAGNs.
Expansion speed <0.1c from symmetry statistics (Scheuer 1995)
BH spin aligns with accreted material in yrs:  stability due to stable accretion
(Natarajan & Pringle 1998)
Mack et al. (1996)
AAS Meeting Wednesday 5th June 2002

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Winged DRAGNs
Multiple outbursts revealed by change of jet axis.
Few % of powerful DRAGNs
What happens if axis does not change?
500 kpc
Multiple orientations imply multiple accretion events, I.e. multiple outbursts, even if the events follow each other quite rapidly as implied by lack of spectrally aged material in some winged dragns, e.g. Dennett-Thorpe et al. (2002).
300 kpc
AAS Meeting Wednesday 5th June 2002

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Bottleneck Lobes
Can get similar structures (not as extreme as in 3C132 from what I’ve seen) from steady jet simulations, due to interactions between jet and eddies in the backflow. So not definitive, but suggestive.
50 kpc
500 kpc
AAS Meeting Wednesday 5th June 2002

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3C390.3
At  26° to line of sight
Twin-peak Balmer lines (Eracleous & Halpern 1994)
Superluminal motion (Alef et al. 1996)
Overlapping lobes
 Extends  0.5 Mpc along line of sight
 Near side (NW) seen 1.8 Myrs more developed:
Bottleneck
More expanded hotspot
265 kpc (projected)
Leahy & Perley (1995)
Angle from fitting balmer lines to disk model.
AAS Meeting Wednesday 5th June 2002

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Power Stability
Hotspots in 80-90% of lobes in powerful DRAGNs  jets nearly always “on”.
Hotspot:lobe flux ratio:
Median 0.22
IQR – 0.54
Jets could fluctuate in power by factors of several.
Best seen as limit to AGN fluctuation, as hotspot structures will fluctuate substantially due to fluid dynamic effects if the simulations are to be believed.
Caveats: “Hotspot” defined as flux within 5% of lobe size, ie scaled to overall size of source. Not the finest scale structure, so some short-term fluctuations averaged out.
From Atlas of DRAGNs
(Leahy, Bridle & Strom 1996)
AAS Meeting Wednesday 5th June 2002

11. Re-invigorated Jets: 3C 33.1
VLA A+B+C+D
20 cm
1.5
Side shocks indicate pre-existing jet cavity is expanding into the lobe. No shock ahead of high-pressure plug shows there is still a jet flow ahead, but with a lower emissivity and presumably pressure. Note there is still a hotspot in this lobe.
200 kpc
AAS Meeting Wednesday 5th June 2002

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Hercules A
Powerful DRAGN in cluster-dominating galaxy at z=
X-ray parameters typical of Abell clusters.
Cluster elongated along radio axis.
400 kpc
Gizani & Leahy (in preparation)
AAS Meeting Wednesday 5th June 2002

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VLA B+C+D
3.6 cm
0.74 beam
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VLA A+B+C+D
6.1 cm
0.36
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J. Morse, STScI
A. Rosen et al. (1999, ApJ)
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Spectral Index 1.5 – 5 GHz
AAS Meeting Wednesday 5th June 2002

17. Understanding the “Rings”
Present in both lobes
Surround jet features
Spectrally young
Brighter on outer side
Brighter in West lobe
Jets:
brighter jet is nearer, from depolarization.
Inclination i  50°
Model:
Jet asymmetry due to beaming:  cos i  0.5
Observed timescales 3x different in the two lobes, from light-travel effect.
Rings are shocks in old lobes caused by new outburst
Fluctuations on many timescales
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VLA B+C+D
3.6 cm
0.74
0.9 Myr
2.7 Myr
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Double-Double DRAGNs
1 Mpc
Prevalence of Double Double structure in Giant radio galaxies suggests larger-amplitude fluctuations on long timescales. Many inner doubles needed to build up outer double.
1 Mpc
Schoenmakers et al. (2000)
Saripalli et al. (2002)
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PKS
ATCA
12 cm
2.9
ATCA
22 cm
6.4
200 kpc
Leahy & Killeen (in preparation)
AAS Meeting Wednesday 5th June 2002

21. Crossing the F-R Divide
Plume best explained as a remnant of previous FR I phase.
Luminosity of PKS :
P178  1025 W Hz-1sr-1 (near FR divide).
Luminosity of plume: ~1023 W Hz-1sr-1
Characteristic of fainter FR I sources.
NB: remnant would be hard to see, if new FRII phase was much brighter.
AAS Meeting Wednesday 5th June 2002

22. Crossing the F-R Divide
Another case: PKS N
Cameron et al. (1988)
Bicknell, Cameron & Gingold (1990)
High resolution:
Clear FR II
With plume
50 kpc
AAS Meeting Wednesday 5th June 2002

23. Crossing the F-R Divide
Another case: PKS N
Cameron et al. (1988)
Bicknell, Cameron & Gingold (1990)
Low resolution:
Plumes form wide-angle tail.
500 kpc
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Death of DRAGNs
Powerful DRAGNs have synchrotron age  10 Myr
typical lifetime ~20 Myr
Few DRAGNs are bigger than 1 Mpc:
Expansion speed ~0.1c 
Max age ~16 Myr?
Jet shutdown:
Hotspots expand, fade
should leave diffuse lobes intact
Fade by synchrotron ageing on ~ 108 yr timescale.
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Dying DRAGNs?
Relaxed steep-spectrum DRAGNs should be more common than “Classical” Doubles.
Actually <10%
Van der Laan (1969):
Age  (Break frequency)-1/2
Detectable if   B
Survey at  should mostly find DRAGNs with   B
Not so!
van Breugel & Fomalont (1984)
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Ghost DRAGNs?
If radio-quiet cavities in clusters are aged relic lobes (e.g. Enßlin 1999), where are the cases visible only in low-frequency images?
Abell 2597
(McNamara et al. 2001)
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Conclusions
Jets show large-amplitude variability on many timescales.
with light-travel effects, will disguise intrinsic symmetry.
Multiple outbursts can dramatically affect large-scale structure of DRAGNs.
End-point of DRAGN lifecycles poorly understood.
AAS Meeting Wednesday 5th June 2002