The observability of recoiling black holes as offset quasars

Transcription

1 The observability of recoiling black holes as offset quasars Laura Blecha! Einstein & JSI Fellow! University of Maryland! with Debora Sijacki, Luke Zoltan Kelley, Paul Torrey, Mark Vogelsberger, Dylan Nelson, Volker Springel, Gregory Snyder, and Lars Hernquist! IAU Focus Meeting: Gravitational Wave Symphony of Structure Formation Honolulu, HI, Aug 12, 2015

2 Gravitational-Wave (GW) Recoil GW beaming imparts a kick to the merged BH! Max kick is ~ 5000 km/s!! (Campanelli et al. 2007, Lousto et al 2012)! For randomly-oriented, high spins, 34% of kicks are > 500 km/s (Lousto et al. 2013)! Wiseman 1992 Kicks are lower if spin alignment occurs prior to merger (more on this later )! (Bogdanovic et al 2007, Dotti et al. 2009, 2012, Kesden et al. 2010, Miller & Krolik 2013)!

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4 Recoiling AGN candidates Kinematic offsets!! see Komossa et al. 2008; Shields et al. 2009; Robinson et al. 2010! Spatial offsets!! see Batcheldor et al. 2010;!! Jonker et al. 2010; Koss, LB et al. 2014! Kinematic and spatial offsets!! see Civano et al. 2010, 12,!! Blecha et al Komossa et al See also! Decarli et al Civano et al Broad/narrow Hβ offset Koss, LB et al. 2014

5 BH spin alignment Spins may be efficiently aligned prior to merger by a circumbinary gas disk (Bogdanovic et al 2007, Dotti et al. 2009, 2012, Miller & Krolik 2013)! Recoil kick velocities depend strongly on progenitor BH spin vectors! Roedig et al 2012 Maximum possible recoil kick is ~ 5000 km/s! Maximum kick with perfectly aligned spins is < 200 km/s!

6 Recoiling BH dynamics:! hydro effects matter 60% gas 10% gas Blecha et al. 2011!! see also: Guedes et al. 2011, Sijacki et al

7 The Illustris Project:! cosmology with moving-mesh hydrodynamics ~ 100 Mpc3 volume! 2 x resolution elements! AREPO code - hydrodynamics solved on an unstructured, moving mesh Vogelsberger et al. 2014a

8 Modeling offset AGN in Illustris 8

9 Modeling offset AGN in Illustris Spin misalignment angle [deg] random-dry random-dry!!!! random-dry random fgas-b!5deg!! fgas-b!!!!!!!!!! aligned!! fgas-b!! hybrid!!5deg 5d log vkick/vesc Randomlyoriented spins Hybrid model:! Nearly aligned spins gas-rich merger = nearly aligned spins, gas-poor merger = random spins 9

10 Spatial and velocity offsets random hybrid aligned Blecha et al. 2015! (arxiv: ) 10

11 Number of observable spatially-offset AGN (per deg 2 ) Random spins 11

12 Number of observable spatially-offset AGN (per deg 2 ) Spatially-offset AGN! (random spins) Volonteri & Madau 2008 Spatially-offset AGN! (random spins) Blecha et al

13 BH merger rate Integrated observed merger rate (log MBH/M > 6, all sky): 0.42 yr -1! Peak rate at z ~ 2! Good agreement with SAMs (e.g., Sesana et al. 2004, Barausse et al. 2012)! But, SAMs have more high-z (& fewer low-z) mergers, also fewer major mergers! Galaxy merger rate in Illustris agrees well with observations (Rodriguez-Gomez et al. 2015)! Stellar & BH mass function, cosmic SFRD, baryonic TF relation, quasar LF also wellreproduced (Vogelsberger et al. 2014b, Genel et al. 2014, Sijacki et al. 2015) 13

14 SDSS quasar spectra Velocity offsets:! random spins Eracleous et al. 2012: 88 QSOs in DR7 with broad Hβ shift Δv > 1000 km/s ~1 per 10 deg 2 with Δv>1000 km/s (SDSS DR7: 9380 deg 2 ) Almost certainly not all are recoils (see also Bonning & Shields 2007, Tsalmantza et al. 2011) 14

15 Number of observable velocity-offset AGN (per deg 2 ) random hybrid aligned 15

16 Number of observable spatially-offset AGN (per deg 2 ) random hybrid aligned 16

17 Summary Offset AGN lifetimes are longest for vkick ~ vesc, such that even seeing-limited observations can resolve spatially-offset AGN. These are promising targets for all-sky surveys.! If spins are randomly oriented, >10 3 spatially-offset AGN could be found in all-sky surveys (PS1-3pi, LSST, WFIRST, Euclid).! Randomly-oriented spins could yield nearly 10 3 velocity-offset AGN in the SDSS footprint; lack of observed offsets is due in part to selection effects but hints at role of spin alignment.! Spin alignment does not eliminate the possibility of detecting recoils unless spins are always highly aligned (within ~5 o ). If spins are aligned only in gas-rich mergers, up to hundreds of spatially-offset AGN could be found in all-sky surveys.! Our results strongly motivate dedicated searches for offset AGN.