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Shock heating by galaxy-scale radio sources

Shock heating by galaxy-scale radio sources. Judith Croston 26 November 2009. Powerful Radio Galaxies: Triggering and Feedback. Overview. Why galaxy-scale radio-loud AGN outbursts are important X-ray observations of radio-galaxy shocks on galaxy scales

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Shock heating by galaxy-scale radio sources

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  1. Shock heating by galaxy-scale radio sources Judith Croston26 November 2009 Powerful Radio Galaxies: Triggering and Feedback

  2. Overview • Why galaxy-scale radio-loud AGN outbursts are important • X-ray observations of radio-galaxy shocks on galaxy scales • What can we learn about radio-galaxy triggering? • What can we learn about radio-galaxy feedback?

  3. Why galaxy-scale sources are important

  4. Galaxy-scale sources • Potentially important for understanding both triggering and feedback. • Two types of galaxy-scale source: • early phase in the life of a full-sized radio galaxy • short-lived outbursts that never evolve to hundred-kpc scales • CSS samples generally dominated by FRII-luminosity objects at high z (e.g. O’Dea 1998) => evidence that shocks are important in ionizing emission-line gas (e.g. Holt et al. 2008) • Handful of low-luminosity galaxy-scale radio galaxies in the local Universe where we observe their impact in detail....

  5. Shocks & radio source evolution • All large radio galaxies must evolve through phase of supersonic expansion => shock heating of environment • Signatures potentially visible in the X-ray (e.g. Heinz, Reynolds & Begelman 1998) => direct measurement of energetic input to environment. • Chandra has failed to find clear evidence for shocks around powerful FRIIs. Scheuer et al 1974

  6. Observations of shock heating on galaxy scales

  7. Centaurus A • Nearest radio galaxy (3.7 Mpc) • Restarting source (outer structures ~600 kpc in projection) • X-ray shell around SW inner lobe (Kraft et al. 2003) 1 kpc

  8. A deep look at the X-ray shell • Cen A VLP data reveal most of the X-ray emission is non-thermal • Spectrum well fitted by a power law with G~2.0, consistent with X-ray synchrotron interpretation. 1 kpc Croston et al. 2009 MNRAS 395 1999 Croston et al. 2009 MNRAS 395 1999

  9. High-energy particle acceleration? X-ray synchrotron emission from SN1006 (Rothenflug et al. 2004) X-ray synchrotron emission at the shock front in Cen A

  10. Broad-band SED Similar to FRI jet knots Similar to SNR • Shock front region so far undetected in the radio, IR (Spitzer) or UV (GALEX). Deeper Spitzer data coming.

  11. Spectral structure Thermal Non-thermal

  12. Shell and lobe dynamics • Thermal part of the shell can be used to investigate shock jump conditions. • Pressure jump of ~10x implies Mach ~2.8 (v ~ 850 km/s) close to the nucleus • Lobe assumed to be isobaric => Pouter/Pism ~ 87, equiv. to Mach ~8.4 (v = 2600 km/s) => tshock ~ 106 y • Inferred expansion speed very similar to SNR with X-ray synchrotron emission (e.g. Vink et al. 2006, Warren et al. 2005, Rothenflug et al. 2004)

  13. B field amplification? • SNR shells inferred to have B fields >> simple compression of the ISM (e.g. Ellison & Vladimirov 2008, Reynolds 2008) => non-linear DSA with B amplification (e.g. Bell & Lucek 2001). • B-field amplification by factors of 10 – 100 plausible in Cen A (Beq ~ 8 mG for k=1 and ~30 mG for k=100) . HESS detection implies B > 7 mG.

  14. HST F814W (red) & F555W (green): VLA 1.5-GHz contours NGC 3801 • z = 0.0113 • disturbed, isolated elliptical • Radio source with very similar morphology to Cen A inner lobes, but no evidence for larger-scale radio structure

  15. X-ray shells in NGC 3801 • Non-thermal model ruled out (strong Fe L complex). • Density jump consistent with strong shock, kT jump => M~ 3 – 4 & expansion speed comparable to inner region of Cen A where no particle acceleration seen. • ETOT ~ 2 x 1056 ergs, equiv. to thermal energy of ISM within 11 kpc – similar to Cen A energetics. Croston et al. 2007 ApJ 660 191

  16. Other possibleshock systems Optical (SDSS) VLA Chandra M~ 2.5 shock NGC 1052 Kadler et al. 2004 A&A 420 467 B2 0838+32A Jetha et al. 2008 MNRAS 391 1052

  17. Shock heating in Seyferts? • ~25 known Seyferts with kpc-scale radio structure – e.g. Hota & Saikia 2006; Gallimore et al. 2006) • New Chandra data reveal bubbles of ~ 0.8 keV gas closely matching the radio structure in NGC 6764

  18. NGC 6764 • X-ray bubbles 2x more luminous than known starburst winds, SFR ~3x lower. • E-W radio outflow from AGN associated with brighter X-ray emission from hotter gas. • Model where disrupted inner jet entrains and shock-heats ISM gas into the kpc-scale bubbles favoured. • Some similar Seyferts: NGC 1068 (Young et al. 2001), M51 (Terashima & Wilson 2001), Circinus? Mrk 6? • Energy in bubbles similar to that in NGC 3801 and Cen A (~ 1055 erg) Croston et al. 2008 ApJ 688 190

  19. What can we learn about radio-galaxy triggering?

  20. Accretion modes Cen A NGC 3801 Evans et al. 2004 ApJ 612 786 Croston et al.2007 ApJ 660 191 Typical LE(R)G FRI nucleus (3C66B) NGC 1052 Kadler et al. 2004 A&A 420 467

  21. Environments • Messy, gas-rich systems : dust lanes, molecular and ionized gas towards the nucleus => recent gas-rich merger (Cen A, NGC 3801 and NGC 1052) • Are powerful galaxy-scale doubles triggered by recent merger & fuelled by cold gas?

  22. Population statistics • Evidence that large quantities of neutral gas and outflows of ionized gas are a feature of galaxy-scale sources (e.g. Emonts et al. 2007, Holt et al. 2008) & that both CSS host galaxies and high-excitation FRIIs have high incidence of merger signatures (e.g. O’Dea 1998, Ramos Almeida talk). • Bright CSS populations have similar nuclear and environmental properties to the local galaxy-scale sources: e.g. in 3CRR 2/16 3CRR CSSs are low-excitation, compared to 25% (35/154) of non-CSS radio galaxies & quasars. • Galaxy-scale sources both locally and at higher z appear to be associated with mergers and fuelled by cold gas, unlike most larger FRIs (see also Röttgering talk).

  23. What can we learn about radio-galaxy feedback? (Conclusions)

  24. Effects of low-luminosity sources • Large amounts of energy are dumped into ISM by small , low-luminosity radio galaxies (e.g. few x 1056 ergs, comparable to thermal energy of ISM) • Effects include: triggered star formation, long-lived compression regions, cosmic ray acceleration, and potentially important effects on magnetic field strength and structure. • There is a significant population of galaxy-scale double sources in local Universe (e.g. ~ 0.02% of SDSS galaxies with z < 0.05, or ~0.06% of ellipticals: Ownsworth et al. in prep) => if taken as duty cycle, implies plausible lifetimes (~105 –106 y) • The dramatic effects seen in a few local galaxy-scale sources are expected in early life of all powerful radio galaxies, while more short-lived outbursts could have occurred in large % of ellipticals

  25. Mechanical feedback from low luminosity sources • Typical sizes of local galaxy-scale sources are ~ 2 – 10 kpc – can only be identified to z~ 0.05 in current radio surveys. • Typical luminosities ~ 1021– 1023 W Hz-1 @ 1.4 GHz, several orders of magnitude below known CSS and GPS populations at high z. • Seyfert radio outflows typically ~ 1 – 2 kpc, and very faint (often difficult to disentangle from star formation), but can nevertheless inject significant energy (~1055 ergs in NGC 6764). • Large low-luminosity population could exist at high z, and could play a role in shutting off star formation as galaxies evolve to the red sequence.

  26. Thanks:Martin Hardcastle, Ralph Kraft, Dan Evans, Preeti Kharb, Ananda Hota & the Cen A VLP collaboration

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