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XMM results in
radio-galaxy physics
Judith Croston
CEA Saclay, Service d’Astrophysique
EPIC consortium meeting, Ringberg, 12/04/05
In collaboration with:
• Martin Hardcastle (Hertfordshire)
• Mark Birkinshaw, Diana Worrall, Elena Belsole,
Dan Evans (Bristol)
• Dan Harris (CfA)
Radio-galaxy morphologies
Outstanding problems
• Magnetic field strengths: can’t be directly measured
from radio synchrotron emission, so equipartition (
min. total energy) commonly assumed
• Particle content: electron-positron or electron-proton?
• Dynamics:
– FRIs: missing pressure?
– FRIIs: supersonic or not?
Solving these problems is essential to understanding
radio-galaxy impact in groups and clusters.
Radio galaxies in X-rays
• Jets and hotspots (typically need Chandra resolution)
• Radio lobes:
–
–
–
–
Non-thermal emission via inverse Compton scattering
Seed photons from CMBR, AGN nucleus and SSC
Measure internal energy density, magnetic field strengths
Infer particle content
• Environments:
– Radio galaxies are found in groups and clusters
– Measure external density and pressure
– Comparison with internal radio-lobe properties to study jet
and lobe dynamics.
– Temperature structure => heating
3C 223
z=0.14
XMM observations of IC
emission from FRII lobes
• Lobe emission from two nearby
FRIIs (Croston et al. 2004, MNRAS
353 879)
• IC scattering of CMB; B ~ Beq
3C 284, z=0.25
• Belsole et al. (2004) found similar
results for three high-z FRIIs
observed with XMM.
• Grandi et al. (2003) detected lobe
emission from Pic A – origin may
be thermal or IC.
Chandra and XMM study
(Croston et al. 2005, ApJ in press, astro-ph/0503203)
• Sample of 33 radio galaxies
observed by Chandra and
XMM.
• Lobe emission from 75% of
sources.
• Magnetic fields between
(0.3 – 1.3) Beq, with peak at
B ~ 0.7 Beq.
• Internal energy always within a
factor of two of minimum
value.
• Energetically dominant proton
population unlikely.
XMM observations of environments
3C 66B
3C 449
• FRI environments show:
Croston et al. 2003 MNRAS 346 1041; 2005
MNRAS 357 279, and Evans et al. 2005
MNRAS, in press, astro-ph/0502183)
– SB deficits at radio lobes
– Dense environments = large,
rounded lobes
– Less dense = narrow plumes
– Heating (see later)
Dynamics and particle content in FRIs
• XMM confirms Einstein/ROSAT results for FRIs:
Pext >> Pint(equipartition)
 extra particle content/departure from equipartition.
• IC upper limit rules out electron domination to provide
additional pressure.
• Thermal upper limit rules out entrained gas with Tenv .
• Heated, entrained material (T ~ 3 – 5 keV) most plausible.
• Relativistic protons possible, but need p/e ~ 200.
FRII environments
• Also detected with
XMM:
– Groups rather than
clusters
– No evidence for
shock-heating
– Pext ~ Pint
(measured from IC)
=> Not
supersonically
expanding?
XMM detects shock heating
• XMM and Chandra
observations show radio-lobe
shock heating of the X-ray
environment from the smallscale lobes of Cen A (Kraft et
al. 2003).
(pictures from Kraft et al. 2003)
AGN in cooling flows
• M87 has thermal substructure associated with
radio lobes (e.g. Belsole et al.
2001).
• Is temperature structure
consistent with models for
counteracting cooling flows
(e.g. Molendi 2002, Kaiser
2003, Ghizzardi et al. 2004)?
=> AGN energy input (rising
bubbles/mixing) can balance
cooling and produces multiphase medium.
Extended heating in FRI atmospheres
• XMM-observed RG
environments
significantly hotter than
LX/TX prediction.
• ROSAT study:
– RL groups hotter than
RQ groups of the same
luminosity.
– 50% of E-dominated
groups (= X-ray bright)
are RL.
(Croston et al. 2005, MNRAS, 357 279)
Ongoing projects with XMM
• Inner jet dynamics
– Testing jet models (Laing & Bridle 2002) by measuring
environmental properties.
– Investigating role of environment in producing stable jets.
• FRI environments
– Completing sample that includes all common morphologies
to understand jet/environment interactions in whole
population.
• Archive study of heating
– Large fraction of ROSAT sample now observed by XMM.
– Follow up heating study with better Lx and Tx constraints,
detailed study of gas distribution in radio-loud and quiet
groups.