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Quasars with a “Kick”

Quasars with a “Kick”. Greg Shields 1 , Erin Bonning 1,2,3 , Sarah Salviander 1 1 U. Texas 2 Obs. Meudon 3 Yale Univ. ApJL, 666, 13 (2007); arXiv:0802.3873. Image: NASA / CXC / A. Hobart. Introduction. Galaxy mergers lead to binary supermassive black holes (BH) and likely mergers.

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Quasars with a “Kick”

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  1. Quasars with a “Kick” Greg Shields1, Erin Bonning1,2,3, Sarah Salviander1 1U. Texas 2Obs. Meudon 3Yale Univ. ApJL, 666, 13 (2007); arXiv:0802.3873 Image: NASA / CXC / A. Hobart

  2. Introduction • Galaxy mergers lead to binary supermassive black holes (BH) and likely mergers. • Numerical simulations predict vrecoil up to 4000 km/s due to anisotropic emission of gravitational waves. • Recoil could displace the BH from the galactic nucleus or eject it from the galaxy. • Possible observational manifestations include galactic nuclei with no BH, wandering BH, wandering AGN, tidal flares

  3. Motivation Image credit: HENZE/NASA

  4. How many big Kicks? • Smooth function of mass ratio, spin magnitude, orientation (many studies) • Baker et al (0802:0416) m2/m1 > 0.25, a = 0.9 v > 500 km/s 62% v > 1000 km/s 25% (Multiply by ~2/3 for line-of-sight velocity.)

  5. Runaway Quasars For BH merger in active QSO, accretion disk remains bound to recoiling BH inside radius where orbital velocity equals recoil velocity: Rb = (1018.1) cm M8v1000-2. Retained disk mass may be sufficient (beware self-gravity) to fuel prolonged QSO activity: Mb = (108.0 M) -1-4/5M83/2 (dM/dt)07/10v1000-5/2 where (dM/dt)0 is the mass accretion rate (M yr-1).

  6. Image: Tim Jones/McDonald Observatory PIO

  7. Get Your Kicks from SDSS • Broad emission-line region (BLR) corresponds to bound disk • Broad lines will be shifted in velocity relative to host galaxy • Narrow emission-line region (NLR) will not follow BH; narrow lines will reflect velocity of host galaxy. • We examined 3000 QSOs from SDSS Data Release 5 (DR5) in the redshift range 0.1 < z < 0.81 with measurable H and [O III] and with successful fits by our automated program. • Objects with shifts > 1000 km/s between H and [O III] peak velocities were inspected for good quality spectra and symmetrical broad lines.

  8. Mg II Hb [O III] z = 0.4650 SDSS J091833+315621: H – [O III] ~ 2700 km/s. Green and black lines represent data before and after Fe II template subtraction; red line shows fit to data.

  9. Recoil Candidates from SDSS • Candidates ruled out for • Large asymmetries in H • Strong Fe II emission z = 0.268 SDSS J123215+132032: an asymmetrical H.

  10. Results --- Incidence of kicks greater than line-of-sight velocity: 0.2% > 800 km/s (Mg II) [beware slowing in galaxy] 0.04% > 2500 km/s (Hbeta) --- Even these kicks are doubtful (spectral details: asymmetry; Mg II v. Hbeta velocity; [Ne V] width). ---The rarity of big kicks could result from a dearth of mergers during an active QSO phase or alignment of BH spins by nuclear gas during the orbital decay (Bogdonavic et al 2007).

  11. Recoil Candidates? Hbeta, Mg II symmetrical, consistent Narrow line details favorable Bonning et al (2007) --SDSS J1348+0524 (-740 km/s) --SDSS J1031+4154 (-490 km/s) Komossa et al (2008 ApJ 678, L81) --SDSS J0957+2943 (-2650 km/s)

  12. Recoil Flares • Marginally bound material will rejoin the moving disk with impact velocity ~ vkick. • The resulting shocks produce a brief but powerful thermal flare with luminosity Lf = (1045.7 erg s-1) -1-4/5M81/2 (dM/dt)07/10v10005/2, with a temperature kT = (0.7 keV) v10002 and duration tf = (103.9 yr) M81/2 v1000-3. The high luminosity results from the large mass and short timescale, even though the binding energy per unit mass is only 10-5 c2. --- Surrounding disk material will largely degrade X-rays to optical-UV emission lines and further to infrared continuum • Roughly 100 flares at redshift < 3 may be in play at one time above vkick = 500 km/s (merger simulations or QSO counts).

  13. Numerical simulation (arXiv:0802:3873) Video at http://astro.as.utexas.edu/~shields/recoil/t65.gif

  14. Conclusions • Recoiling black holes could retain a massive accretion disk. • The disk could fuel a lasting QSO phase while the BH wanders far from the galactic nucleus. • The violent infall of material into the recoiling disk produces a brief but powerful thermal flare whose appearance depends on reprocessing. • Shifted broad lines in QSOs may reveal recoiling QSOs, but most shifts result from conditions in the BLR. The true incidence of kicks over 1000 km/s is less than theoretically expected for rapidly spinning holes with random orientations and similar masses. This could result from a dearth of mergers during an active QSO phase or alignment of BH spins by nuclear gas during the orbital decay.

  15. References • Numerical relativity: Baker et al arXiv 0802:0416 and references therein; Dain et al. 0803.0351 • Wandering QSOs: Madau & Quataert (2004) ApJ 606, L17; Loeb (2007) PhysRevLett 99.041103 and references therein; Shields et al. 0707.3625; Bonning et al. (2007) ApJ 666:L13; Komossa et al. (2008); Blecha & Loeb 0805:1420 • Recoil flares: Shields et al. 0707.3625; Lippai et al ApJ (2008) 676:L5; Shields & Bonning 0802.3873; Schnittman & Krolik 0802:3556. • Tidal flares: Komossa & Merritt 0807.0223

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