Radio galaxies in the Chandra Era, Boston, July 2008

Shock heating in the group atmosphere of the radio

galaxy B2 0838+32ANazirah Jetha1, Martin Hardcastle2, Trevor Ponman3, Irini Sakelliou4

1 IRFU, CEA-Saclay, 2University of Hertfordshire, 3University of Birmingham, 4MPIA-Heidelberg, Germany

Radio galaxies in the Chandra Era, Boston, July 2008

Radio Galaxy Heating

• Two major unresolved problems:– Similarity breaking -- groups and clusters

follow scaling relations, but different from self-similar predictions.

– Lack of very cold gas in group and galaxy cores

• Increasing evidence that radio galaxies can heat IGM

RLRQXMM RGs

Croston et al. 2008 MNRAS 386 1709

Radio galaxies in the Chandra Era, Boston, July 2008

Radio Galaxy Heating

• On small scales, radio galaxies can heat via shocks generated by overpressured rapidly expanding lobes, e.g. Cen. A (Kraft et al 2003), NGC 3801 (Croston et al 2007).

• As radio source evolves, heat is transferred in different ways (Reynolds et al, 2002; Kraft et al, 2003; Nusser et al, 2006 )

• Evidence to suggest that repeated cycles of radio galaxy heating have a significant effect (Croston et al, 2005; Jetha et al, 2007).

Radio galaxies in the Chandra Era, Boston, July 2008

Radio Galaxy Heating

• In order to explore effects of multiple cycles, wantsystems where more than one outburst can be studied simultaneously

• And ideally want systems:– Showing the ‘extremes’ of the AGN cycle– Sufficiently distant to study large scale IGM– Close enough to study small-scale shocks– ‘Simple’ enough that effects of multiple outbursts

can be disentangled.

Radio galaxies in the Chandra Era, Boston, July 2008

80kpc

1.4 GHz. (Jetha et al sub.)

0838+032 - Radio

2.5 kpc 85 ks Chandra observation to:

• Investigate potential shocks around small scale source.• Examine effects of heating on large scale environment.

Radio galaxies in the Chandra Era, Boston, July 2008

0838+032 - X-ray

•SDSS OPTICAL

•5 GHz VLA

• Chandra X-ray

Host galaxy

Companion galaxy

Companion galaxy

Shock

Radio galaxies in the Chandra Era, Boston, July 2008

0838+032 - X-ray

• Group emission out to ~130 kpc

• Shock temperature:

• Mach number:

Radius (kpc)0.12 130

Cou

nts

arcs

ec-2

100

Radio galaxies in the Chandra Era, Boston, July 2008

Timescales of the source

• Radius of inner lobes - 4.3 kpc

• Speed of sound in group - 330 km s-1

• Age - 3.4 - 6.5 Myr

• Spectral age of outer lobes ~50 Myr

• Dynamic age, assuming lobes inflated in situ - 200 Myr

• Infer old lobes switched off ~150 Myr ago

Radio galaxies in the Chandra Era, Boston, July 2008

Feedback induced shocks?

• Central cooling time of gas - 170 Myr

• Comparable to time between old outburst switching off and new outburst switching on

• No indication in AGN spectrum for absorption from cold material to suggest merger (c.f. Cen. A, Kraft et al 2006; NGC 3801, Croston et al 2007)

Radio galaxies in the Chandra Era, Boston, July 2008

Energetics of inner lobes

• Mechanical power output of new source - (5.4 - 62) x 1037 W

• No evidence for cold gas, so assume that AGN is accreting in hot-mode.

• Calculate Bondi power - PBONDI ~ 6 x 1037 W

• Lower limit due to constraints on black hole mass and measuring density at Bondi radius.

Radio galaxies in the Chandra Era, Boston, July 2008

Energetics of outer lobes

• NW lobe is 130 kpc and S lobe is 190 kpc from centre

• Model lobes as ellipsoids with negligible initial volume inflated in situ

• Obtain pressure from density profile

• PdV work done on IGM - (2 - 4)x1051 J

• Mean energy input rate - 3x1035 - 3x1036 W

• Bolometric X-ray luminosity (3.2±0.2)x1035 W

Radio galaxies in the Chandra Era, Boston, July 2008

Implications for feedback models (1)

• Sufficient energy to counteract cooling

• Observations of lobes indicate delay in turning off cooling

• Due to time for energy/entropy to transfer to where needed

• Or time to drain accretion flow:–

Radio galaxies in the Chandra Era, Boston, July 2008

Implications for feedback models (2)

• What about to turn accretion on again?• Central gas cooling time and time between

outbursts is comparable• Time taken for gas to cool may determine off

time• Clear that relationship between the two

timescales determines duty cycles and on-times for any given system

Radio galaxies in the Chandra Era, Boston, July 2008

Conclusions

• 0838+32A - restarting radio source driving overpressured bubbles into IGM

• Old lobes have done sufficient work to counteract radiative cooling

• Young lobes driving a shock into IGM• No evidence for merger to trigger new lobes• Time delay in stopping accretion related to energy

transfer/flow draining and microphysics of system • First known system where strong shocks around

young lobes are plausibly driven by hot-gas accretion (feedback)