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Shock heating in the group atmosphere of the radio galaxy B2 0838+32A

This study explores the heating effects of radio galaxies on the intergalactic medium (IGM), focusing on the case of the radio galaxy B2 0838+32A. The research examines the potential shocks generated by the expanding lobes of the radio source and investigates the impact of heating on the large-scale environment. The findings suggest that the radio galaxy's shocks, driven by hot-gas accretion, play a significant role in counteracting cooling and maintaining the cycle of activity.

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Shock heating in the group atmosphere of the radio galaxy B2 0838+32A

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  1. Shock heating in the group atmosphere of the radio galaxy B2 0838+32A Nazirah 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

  2. RL RQ XMM RGs Croston et al. 2008 MNRAS 386 1709 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 Radio galaxies in the Chandra Era, Boston, July 2008

  3. 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

  4. 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

  5. 2.5 kpc 80kpc 1.4 GHz. (Jetha et al sub.) 0838+032 - Radio • 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

  6. Host galaxy Companion galaxy Shock Companion galaxy 0838+032 - X-ray • SDSS OPTICAL • 5 GHz VLA • Chandra X-ray Radio galaxies in the Chandra Era, Boston, July 2008

  7. 0838+032 - X-ray • Group emission out to ~130 kpc • Shock temperature: • Mach number: 100 Counts arcsec-2 0.12 130 Radius (kpc) Radio galaxies in the Chandra Era, Boston, July 2008

  8. 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

  9. 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

  10. 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

  11. 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

  12. 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

  13. 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

  14. 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) Radio galaxies in the Chandra Era, Boston, July 2008

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