What do
X-shaped Radio Galaxies
have to say about
Radio-Mode Feedback?
Edmund Hodges-Kluck
Chris Reynolds (UMd), Teddy Cheung (NRL),
Cole Miller (UMd), Marc Pound (UMd)
Clusters & Groups in the Chandra Era
Agenda
What are X-shaped Radio Galaxies?
The origin of XRGs
XRGs and Ghost Cavities
“Normal” Double-Lobed (FR II) Radio Galaxies
Hot Spots
Lobes
Jets
X-shaped Radio Galaxies (~5% of RGs)
Long, Inactive Lobes
(Leahy+84)
Centro-symmetric
(Leahy+84)
Weak FR IIs/Strong FR Is
(Cheung+09)
Higher than average
SMBH masses
(Mezcua+10)
Possibly related to
“winged” RGs
(Cheung 07)
Jets co-aligned with
host major axis
(Capetti+02)
What are X-shaped Radio Galaxies?
The origin of XRGs
XRGs and Ghost Cavities
1. Fossil Relics
• Precession (Dennett-Thorpe+02)
• SMBH merger (Merritt+02)
• Accretion torque (Rees+82)
2. Redirected Lobes
• Buoyant Backflow (Worrall+95,
Leahy+84)
• Overpressured Cocoon (Capetti+02)
3. Binary AGN
• Twin jet pairs (Lal+Rao 05)
X-ray Imaging
Radio
lobes are bubbles in
Do the data
a 7role
a tenuous,
hotsupport
(T > 10
K)
for XRG environments?
plasma
Hydrodynamic Simulations
Radio
X-ray
If jets/lobes interact with
Is the hydrodynamic
surroundings,
it will be
hypothesis plausible?
with the IGM/ICM
Hodges-Kluck+2010a ApJ…710.1205
ISM
IGM
ΔPA = 0 Coaligned with major axis
ΔPA = 90 Coaligned with minor axis
Hodges-Kluck+Reynolds 2011ApJ…733…58
X-ray observations
and
hydrodynamic simulations
support a role for XRG
environments
Unclear whether proposed
hydrodynamic models really work
At least one XRG looks like a spin-flip:
4C +00.58
(Hodges-Kluck+2010b ApJ…717..L37)
Review: Gopal-Krishna+2010 arXiv/1008.0789
What are X-shaped Radio Galaxies?
The origin of XRGs
XRGs and Ghost Cavities
What Happens to Dead Radio Galaxies?
How do radio galaxies heat cores?
• PdV energy in cavities vs.
jet-driven shocks (e.g. Reynolds+02),
disk winds (e.g. Gaspari+11)
• Maybe they don’t directly? Hybrid
conduction models; Stirring
(Ruszkowski+Oh 2010)
Ghost cavities reported
in a number of systems
(e.g. Perseus, NGC 741, A2597)
Cavities ubiquitous in groups; little
correlation with radio emission
(Dong+10), but only seen near cores
(c.f. Giacintucci+11)
Cavity evolution poorly understood
Inactive Lobes
100 kpc
• Long (up to >100 kpc)
• Usually in groups
• Either fossils or evolve in response to environment
• Presumably have cavities
• Bright at 1.4 GHz
Only 2 XRGs have X-ray exposures of ~100ks:
Chip Edge
Jet
Both have significant cavities associated with wings
(highlighted in unsharp mask images)
Proof of concept: NGC 326
0.3-3 keV
3-8 keV
The east wing cavity is ~100 kpc from the core and is
probably over 50 Myr old
The active outburst may itself be associated with cavities
and a shock front…
kT (apec 1-T 0.3-5 keV)
Surface Brightness
1. Temperature does not follow surface brightness
2. Density, temperature changes behind front consistent with
Mach ~2 shock
Raw 0.3-5 keV binned 16x
Unsharp Mask
What can we know?
What can’t we know (yet)?
• Age from several avenues
• Filling factor/entrainment
• Rough size/energy
• Cap of material?
• Gross magnetic structure (Murgia+01)
• Old shocks/sound waves?
• T/P of surrounding gas
• Bubble shredding?
• Detailed synchrotron map
Need higher S/N!
Summary
XRGs are an interesting subclass of doublelobed radio galaxies whose origin is mysterious
XRGs illuminate hard-to-find “dead” radio bubbles far from the
AGN
Higher S/N required to study cavities (XMM? Astro-H?)
3C 388
3C 305
3C 264
3C 171 3C 465 3C 272.1 3C 120
Old cavities re-energized by restarted
AGN in hydro simulations
Jet Axis
False Synchrotron (GHz)
Wing length as a function of
atmosphere parameters
Wing length as a function of
jet parameters
4C +00.58
Case in Point: 4C +00.58
Radio jet aligned with
host minor axis, wings
very long relative to
cocoon
Radio
Optical
Case in Point: 4C +00.58
“Stellar shell” suggests
recent minor galaxy
merger
X-ray cavities aligned
with wings and major axis
suggest recent jet
activity along other axes
Optical
Long wings preclude
hydrodynamic
deflection—they must be
fewer than 40 Myr old
X-ray
unsharp
mask
Case in Point: 4C +00.58
 ~ 1.6
 ~ 0.6
The bent jet, seen in radio (VLA
+ CARMA) and X-ray (Chandra),
appears to be cooling rapidly at
the tip: has it been dragged?
Hypothesis: A minor merger activated the radio
galaxy along one axis, then accretion torque or
coalescence of a SMBH binary moved the jet.
Model Testing with Timescales
 Minimum wing age (transonic expansion)
texp
l

~ 90 Myr (measured from X-rays, radio)
cs
 Maximum Cocoon Age (transonic expansion)
texp
l

~ 35 Myr (measured from X-rays, radio)
cs
 Synchrotron cooling time (wing decay)
t sync
me c 2
E
  4
~ 40 Myr (measured from radio)
2 2

E 3  T c  U B
 X-ray free-free (cavity wall) cooling time
E 5 nkT
t ff  
~ 500 Myr (measured from X-rays)

E 2 n(T )
Did the wings form hydrodynamically?
 Transonic expansion time
(minimum age):
 texp ~ lwing/cs~ 90 Myr
 tsync ~ 40 Myr [1 GHz]
 Cocoon should expand faster
than wings, and cs is
constant in the region—
strong projection ruled out
by OII/OIII ratio
 Cocoon is well defined
 Cocoon texp < 35 Myr
 Cavities misaligned with the
jets unexplained
SDSS r+g
Timescales
 Sound speed (pressure crossing time)
cs 
kT
~ 400 km/s

 Temperature and emission-weighted density from apec fits to
the 0.3-3 keV spectrum in Xspec
 kT ~ 1.0 keV within 40 kpc (approximately isothermal)
 Synchrotron (wing) cooling time
t sync
me c 2
E
  4
~ 40 Myr (measured from radio)
2 2

E 3  T c  U B
 Equipartition B-field assumed; use radio flux and volume of
wings/lobes, with spectral index (~0.7) determined from
photometry
 With B in hand, synchrotron frequency measured at 1.4 GHz,
so wing lifetime is for electrons radiating at 1.4 GHz
Timescales
 X-ray free-free (cavity wall) cooling time
E 5 nkT
t ff  
~ 500 Myr (measured from X-rays)

E 2 n(T )
 Temperature and emission-weighted density from apec fits to
the 0.3-3 keV cavity wall spectrum in Xspec
 Assume a typical bremsstrahlung cooling function (T0.5)
 Maximum Cocoon Age (transonic expansion)
texp
l

~ 35 Myr (measured from X-rays, radio)
cs
 Cocoons associated with bow shocks, powerful jets, so
supersonic expansion (several times ambient sound speed)
assumed even in weaker radio galaxies
 Trans- or sub-sonic expansion unlikely to produce a cocoon,
but possibly intermittent jets…