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Hot and Cold Gas Accretion Modes and Feedback Processes in Radio-loud Active Galaxies

Dan Evans (Harvard) Martin Hardcastle (U. Hertfordshire) Judith Croston (U. Hertfordshire). Hot and Cold Gas Accretion Modes and Feedback Processes in Radio-loud Active Galaxies. Radio Galaxy. Standard Picture of Radio-Loud AGN. Luminous accretion disk surrounded by “torus”

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Hot and Cold Gas Accretion Modes and Feedback Processes in Radio-loud Active Galaxies

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  1. Dan Evans (Harvard) Martin Hardcastle (U. Hertfordshire) Judith Croston (U. Hertfordshire) Hot and Cold Gas Accretion Modes and Feedback Processes in Radio-loud Active Galaxies

  2. Radio Galaxy Standard Picture of Radio-Loud AGN • Luminous accretion disk surrounded by “torus” • X-ray continuum emission in the nuclei of RL AGN consists of: • “Radio-quiet” accretion-related component • “Radio-loud” jet-related component Which dominates the X-ray emission?

  3. The Fanaroff-Riley Dichotomy • Is the dichotomy • Environmental? • Interaction of the jet with ambient medium either causes the jet to decelerate (FRI) or propagate supersonically to large distances (FRII) • Intrinsic? • Properties of the central engine govern large-scale morphology (FRI/FRII)

  4. Low- and High-Excitation Radio Galaxies Based on strength of high-excitation lines , e.g., [OIII] (Laing et al. 1994) • FRIs are almost entirely low-excitation • Significant population of low-excitation FRIIs at 0.1<z<0.5 • Encompass all NLRGs and BLRGs • Almost entirely FRIIs • A handful of FRIs, too

  5. 3CRR z<0.5 Sample Results e.g. 3C 264 (LERG FRI) • Chandra observations of the nuclei of 40/86 z<0.5 3CRR sources • X-ray emission of LERGs is dominated by a parsec-scale jet, with little or no intrinsic absorption • X-ray emission of HERGs is dominated by an accretion flow and is heavily absorbed (except BLRGs) • Each HERG also has an unabsorbed component of X-ray emission  jet origin • See Evans et al. (2006, ApJ, 642, 96); Hardcastle et al. (2006, MNRAS, 370, 1893) Jet e.g. 3C 403 (HERG FRII) Jet Accn

  6. Where is the torus in LERGs? • Cannot determine presence or absence of torus directly • Assume there exists a ‘hidden’ accretion component obscured by a torus of intrinsic absorption 1023 atoms cm-2 • Find upper limits to luminosity of accretion-related emission • Data don’t exclude luminosities of LX,acc ~ 1039-1041 ergs s-1 (X,Edd ~ 10-7-10-5) • Substantially lower than HERGs, LX,acc ~ 1043-1044 ergs s-1 (X,Edd ~ 10-3-10-2) • Implies accretion flow radiatively inefficient (e.g., ADAF) Jet Accretion e.g. 3C 274 (M87)

  7. Luminosities • For a given 178-MHz radio power, LERGs produce significantly less radiative accretion luminosity • Pointing to a dichotomy in the excitation properties of AGN? i.e., not a nuclear F-R dichotomy White = LERGRed = NLRG Green = BLRG; Blue = quasar Circle => FRI Line goes through FRII NLRG Limits assume NH = 1023 cm-2

  8. Low state High state Speculation: Hot vs. Cold Accretion Low-exc Hi-exc • Fundamentally different accretion mode in LERGs and HERGs • HERG features (disk, torus, etc.) require cold fuel • Could LERG features (radiatively inefficient accretion, ADAF) require a hot gas supply? • Could all LERG be powered by ‘hot-mode’ accretion and all HERG by ‘cold-mode’? • Discussed in detail by Hardcastle et al. (2007, astro-ph/0701857) LX Accretion flow Jet Esin et al. (1997); Körding, Falcke, & Markoff (2002) mcrit mEdd m Allen et al. (2006) Bondi accretion vs. jet power in nearby cluster-center radio galaxies (Allen et al 06)

  9. Testing Hot-Mode Accretion Compare Bondi accretion power with jet power

  10. Testing Hot-Mode Accretion Compare Bondi accretion power with jet power Black hole mass vs. K-band bulge luminosity for spirals and ellipticals (Marconi & Hunt 2003)

  11. Testing Hot-Mode Accretion • Assume central environment of all sources is similar to 3C 31 • Good approximation for LERGs • HERGs likely to have less galaxy-scale gas (Croston et al. in prep.) Compare Bondi accretion power with jet power Density as a function of radius for model fits to X-ray observations of 3C31 (Hardcastle et al. 2002)

  12. Testing Hot-Mode Accretion • Inflating cavities • e.g. Allen et al. (2006) Compare Bondi accretion power with jet power Models of jet deceleration e.g. Laing et al. (2002) Willott et al. (1999) relation

  13. Bondi rates • FRI sources (circled) lie close to the line of equality, as expected from earlier calculations • Many LERG FRIIs lie close to the line too • The majority of HERGs are a long way away from being able to be powered by hot-mode accretion --> additional (cold) gas needed

  14. Both FRI and FRII kpc-scale structures can be produced by nuclei with low accretion luminosity (LERGs) • Conversely, FRIs and FRIIs can be produced by HERGs • FRI/FRII dichotomy entirely due to environment and jet power • Excitation dichotomy controlled by accretion mode 3C 388 (LERG FRII) Kraft et al. (2006) Cen A (HERG FRI) Kraft et al. (2002)

  15. True ‘feedback’ between AGN and hot phase requires the AGN to be controlled by the hot phase.Only directly possible in hot mode • In cold mode accretion the radio source can blow away its atmosphere without affecting its fuel supply • Consistent with observations of FRIIs in poor environments which show work done/energy stored comparable to total thermal energy of atmosphere 3C 33 (HERG FRII) Kraft et al. (2007)

  16. Hot-mode sources need massive central black holes and a good supply of hot gas – they will tend to inhabit the most massive galaxies in relatively rich environments • Cold-mode sources’ power comes from accretion of cold gas so they can inhabit poorer systems. Merger activity important • Qualitatively good agreement with known facts 3C 66B (LERG FRI) Croston et al. (2003) Cen A (HERG FRI)

  17. Summary • The excitation of an AGN is a vital parameter in unification schemes • X-ray emission of LERGs is unabsorbed and dominated by a parsec-scale jet • X-ray emission of HERGs is heavily absorbed and accretion-related • Bondi accretion of hot gas sufficient to power LERGs • Bondi accretion of hot gas insufficient to power HERGs • Additional supply of cold gas need to power HERGs • The Fanaroff-Riley dichotomy remains a consequence of the interaction between the jet and the environment

  18. Jet Luminosity-Luminosity Correlations • Consider LX and LR • Considerable scatter • Strong LX-LR correlation for unabsorbed X-ray components • Suggests X-ray emission affected by beaming in same manner as radio • Origin of X-ray emission in pc-scale jet (outside any torus) Jet

  19. Luminosity-Luminosity Correlations • Components with NH ~ 1023 lie above trendline • As does 3C 390.3, unobscured BLRG • All have Fe K lines • Accretion-dominated and surrounded by a torus • HERGs are dominated by these components Jet NH≤ 5 x 1022

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