1. Shock heating by galaxy- scale radio sources Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback

2. 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 What can we learn about radio-galaxy triggering? What can we learn about radio-galaxy feedback? 2

3. Why galaxy-scale sources are important

4. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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.... 4

5. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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. 5 Scheuer et al 1974

6. Observations of shock heating on galaxy scales

7. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 1 kpc 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)

8. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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  ~2.0, consistent with X-ray synchrotron interpretation. Croston et al. 2009 MNRAS 395 1999 1 kpc Croston et al. 2009 MNRAS 395 1999

9. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback Shock front region so far undetected in the radio, IR (Spitzer) or UV (GALEX). Deeper Spitzer data coming. Similar to FRI jet knots Similar to SNR Broad-band SED

11. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback Thermal Non-thermal Spectral structure

12. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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 => P outer /P ism ~ 87, equiv. to Mach ~8.4 (v = 2600 km/s) => t shock ~ 10 6 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) Shell and lobe dynamics

13. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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 (B eq ~ 8  G for  =1 and ~30  G for  =100). HESS detection implies B > 7  G. B field amplification?

14. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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 HST F814W (red) & F555W (green): VLA 1.5-GHz contours

15. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback Croston et al. 2007 ApJ 660 191 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. E TOT ~ 2 x 10 56 ergs, equiv. to thermal energy of ISM within 11 kpc – similar to Cen A energetics.

16. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback Optical (SDSS) VLA Chandra Other possible shock systems M ~ 2.5 shock B2 0838+32A Jetha et al. 2008 MNRAS 391 1052 NGC 1052 Kadler et al. 2004 A&A 420 467

17. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback ~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 Shock heating in Seyferts?

18. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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 (~ 10 55 erg) NGC 6764 Croston et al. 2008 ApJ 688 190

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

20. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback Evans et al. 2004 ApJ 612 786 Accretion modes Cen ANGC 3801 NGC 1052 Typical LE(R)G FRI nucleus (3C66B) Kadler et al. 2004 A&A 420 467 Croston et al.2007 ApJ 660 191

21. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback Effects of low-luminosity sources Large amounts of energy are dumped into ISM by small, low-luminosity radio galaxies (e.g. few x 10 56 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 if taken as duty cycle, implies plausible lifetimes (~10 5 –10 6 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. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback 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 ~ 10 21 – 10 23 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 (~10 55 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. Mechanical feedback from low luminosity sources

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

27. Judith Croston 26 November 2009 Powerful Radio Galaxies: Triggering and Feedback Radio X-ray Width & location of the shock front