Pulsar Timing and Galaxy Evolution

1. Common Ground in the GWB Pulsar Timing and Galaxy Evolution Sarah Burke Swinburne University/ATNF ATNF GW Mtg December 12, 2008 Supervisors: Matthew Bailes, David Barnes, Simon Johnston, Dick Manchester In collaboration with: Dick Manchester, Ron Ekers, Chris Phillips

2. CLAIM Pulsar timing should detect GW emission from binary supermassive black hole (SMBH) systems at sub-pc separations Supermassive: mBH > ~106 MSun

3. GWB A background of emission from hard binaries Supermassive systems with BH mass ratio >0.3 Porb = 106 - 108 s Contributing population anywhere from z = 0 to high redshift (z > 6) Single source Nearby (z<1) Porb = 106 - 109 s Very close orbital separation; a < ~0.1 pc GW detection from PTing All binary black holes must have been formed via a galaxy merger and undergo subsequent inspiral processes before reaching the pulsar regime.

4. The modelling approach • How many merged galaxies exist? - How many galaxies containing SMBHs are merging? - What is the BH mass function? - When/where in the universe did the merger happen? • What is the timescale for inspiral, coalescence of a resulting SMBH binary?

5. Stochastic GWB Sources Characteristic Strain Gravitational wave frequency

6. A long way to go! • “Last parsec” problem is still unresolved! • Binary SMBH populations unknown • Even at earlier stages of binary evolution • Hierarchical models vs. Monolithic • No local binary black holes to test GR theory and pulsar timing methods.

7. CLAIM Identification of SMBH binary systems in local galaxies will be beneficial to pulsar timers and galaxy evolutionists Thus far, all binary evidence has been tenuous and (nearly) all claims for binaries have been indirect

8. Binary Detection Methods Et cetera

9. A robust, direct binary BH detection method • Exploitation: • Unique spectral energy distribution of AGN • Relation of AGN to BHs (Ron’s talk) • Existence of double, compact flat/inverted spectrum sources not yet explored • Combined with: • High-frequency selection favours AGN (AT20G) • Good LBA resolution (~1 mas)

10. 0402+379 Rodriguez et al. 2006 log amplitude Double nucleus log frequency Direct Detection: Spatially Resolved Systems log amplitude log frequency

11. VLBI Parameter space 2-point correlations CLASS Galaxy merger rates Number AT20G Pulsar timing sensitivity Chance radio, xray double detections 0 1 10 100 1000 1e4 1e5 1e6 1e7 1e8 ---> Linear separation between most massive galactic BHs (pc) Integrated over redshift bin and BH mass range

12. Parameter space Galaxy groups, large scale clustering, chance projeted separations Bound, merging galaxies/halos Number Bound binary BH systems Massive objects falling to centre; dynamical friction 0 1 10 100 1000 1e4 1e5 1e6 1e7 1e8 ---> Linear separation between most massive galactic BHs (pc) Integrated over redshift bin and BH mass range

13. Binary hardening Where things get interesting 3-body interactions with stellar background Loss cone depletion Number Dynamical friction GW emission; final inspiral Jaffe and Backer (2003): N  a13/2 0 1e-3 1e-2 0.1 1 10 100 1000 1e4 1e5 BH separation

14. Hard binary stage: longer than a Hubble time? DANGER! NO astrophysical gravitational wave background! Number Stall region? 0 1e-3 1e-2 0.1 1 10 100 1000 1e4 1e5 BH separation Where things get interesting Efficient loss-cone repopulation

15. Aiming for results Sources in a GW regime that will coalesce in t = 1/H0 (H0 = 72 km/s/Mpc) LBA resolution limit VIPS resolution limit

16. Preliminary Counts • CLASS • Imaging and spectral indices of ~10000 flat-spectrum sources • 149 sources with multiple flat-spectrum components identified • 22 identified as gravitational lenses

17. Preliminary Counts Australia Telescope 20GHz Survey Short-long baseline Visibility ratio Blue: spectral index -0.5 Yellow: spectral index -0.3 Rajan Chettri, Ron Ekers

18. Preliminary Counts CLASS At the moment… a little bleak N 10 30 50 70 90 110 130 0402+379 NGC6240 0 1e-3 1e-2 0.1 1 10 100 1000 1e4 1e5 BH separation

19. Science aims • Pulsar timing: • Possible discovery of individual GW-emitting sources • Observationally constrained parameters/scenarios in GWB models • Stochastic GWB power spectrum based on actual sources or predictions from counts • With any detections, can put a lower limiton the GWB for pulsar timing. • Direct evidence for close binary black holes and black hole coalescence

20. Science aims • Merger dynamics & MBH Evolution: • Observational check of hierarchical galaxy formation models • Local binary population count • Discovering new BH systems: ability to study host galaxies and post-merger dynamics, timescales.

21. (END)

22. Outline of talk • 1. The problem & background • Pulsars detect binaries in a unique frequency range • Binary populations unknown • GWB models are very unconstrained • Galaxy evolution models are very unconstrained • 2. How we’re approaching • CUT TO THE CHASE: • Direct observations of BHs are possible! • And will give science. Show N vs a plots, or some a/adot vs a plots. • 3. What will result • No detections: various interpretations; BHBs do not exist, or only exist only for very short periods of time. • An OBSERVED lower limit for a GWB (statistical or actual)