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Square Kilometre Array (SKA) — an era of discovery & precision astrophysics

Square Kilometre Array (SKA) — an era of discovery & precision astrophysics. Joss Bland-Hawthorn Anglo-Australian Observatory. Outline. Precision cosmology — comment Structure of SKA science case — missing themes? Accretion history of the Universe Reaching the magnetized cosmic web

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Square Kilometre Array (SKA) — an era of discovery & precision astrophysics

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  1. Square Kilometre Array (SKA) —an era of discovery & precision astrophysics Joss Bland-Hawthorn Anglo-Australian Observatory

  2. Outline • Precision cosmology — comment • Structure of SKA science case — missing themes? • Accretion history of the Universe • Reaching the magnetized cosmic web • Feedback through the ages • Cosmic magnetism — comment • Probing the Dark Ages — some nice tricks! • SKA + VLBA — zooming in on a black hole • SKA + (space)VLBI — complementing GAIA • Time domain + IDV — complementing LSST • Astrometry • MHD revolution and physical processes • High polarization purity at all wavelengths • Consistent (u,v) coverage / beam size at all wavelengths • Desperate need for far more theory • Summary • Which style of science tends to survive? • Need for a Design Reference Mission • Decide on a few key technologies then let engineers do their job! SKA 2004 Penticton, July 20

  3. Precision Cosmology Rapid convergence to an accurate mathematical model… without physical understanding (analogy with QM) e.g. our current perception of inertia requires that we integrate beyond the observable horizon! Our cosmological models are barely predictive, and may never be until arriving at a “theory of everything” So work hard to get errors to < 1% until we see “Mercurial effect” (analogy with GR) … decades of work for SKA

  4. Structure of SKA science case • Are we missing a big theme? • Probing the Dark Ages • Cosmic magnetism • Large-scale structure, galaxy evolution and dark energy • Gravity: pulsars and black holes • Protoplanetary disks, organic molecules, SETI • Why not consider: • Accretion history of the Universe: • Mass structure formation & evolution of IGM, clusters, galaxies • Origin of B field, ang. momentum, reaching the magnetized cosmic web! • Clusters — continuum polarization • Galaxies — HI mapping • Themes then become • Probing the Dark Ages — first stars and black holes • Large-scale structure and dark energy — CMB scales • Accretion history of the Universe — mass structure & spin, magnetized cosmic web SKA 2004 Penticton, July 20

  5. Accretion history of the Universe Accretion: hot, warm or cold? Do cooling flows really exist? SKA 2004 Penticton, July 20

  6. Fundamental limitation of optical/IR cosmology At high z, we are looking at light weighted, metal rich cores where gas reaches solar yield in less than a billion years (Hammann & Ferland 1999) This is a basic flaw of contemporary optical/IR cosmology (Freeman & JBH 2002) CDM models: All groups failed to predict number counts in redshift desert, z=1-2!

  7. Cold, quiescent accretion It’s a real mystery how cold, thin disks form

  8. Cold accretion in action To learn about galaxy formation, need to see “stuff” at large radius where timescales are long… gas! Yun et al SKA 2004 Penticton, July 20 M81 — M82 — NGC 3077

  9. Stellar record • Accretion history written in the stars • But very hard to read without kinematics…… HI gas! SKA 2004 Penticton, July 20 Virgo cluster

  10. M31 halo at 770 kpc -- deepest ever stellar work: 80 hrs on HST ACS to V=31 (Brown et al 03, ApJL) Only way to understand how galaxy formation depends on environment is to do same out to 20 Mpc Accretion history must surely depend on local CDM density field, but impossible to tell without full stellar record and deep HI surveys Stars will be a major theme of ELTs, JWST, and many survey machines HI at all redshifts must be a major theme of SKA! Stellar populations out to 20 Mpc SKA 2004 Penticton, July 20

  11. Hot accretion — central tenet of GF • History: Hoyle 1953, Binney 1977, Rees & Ostriker 1977, Silk 1977, White & Rees 1978, White & Frenk 1991… • Hot accretion remains untested — does it even exist? SKA 2004 Penticton, July 20

  12. Do cooling flows exist? It may come down to B field structure & orientation… SKA 2004 Penticton, July 20

  13. Hydra Polarized radio lobes to measure cluster fields THE END Need to deliver high quality RM on 10-100 pc scales, constant beam size with , polarization purity better than 30 dB

  14. Reaching down to the magnetized cosmic web?

  15. Reaching down to the cosmic web? M31 — M33 HI bridge? SKA 2004 Penticton, July 20 Braun & Thilker 2004

  16. Cosmic magnetic field

  17. Cosmic Magnetism: Looking for Cosmic Faraday Rotation? Things to watch for: solar motion increases E, B and aberrates positions/angles on sky; d/d modified by 1+(v/c) cos ; Galactic foreground! What about local IGM? For single source, magnetized wake hard to detect even at 100 cm • = m2 RM = 812 m2 ne BG Lkpc = 103 10-2 10-4 3 3 = 0.01 radian Milky Way SKA 2004 Penticton, July 20

  18. Probing the Dark Ages ...with a little help from Nature Chris Carilli showed earlier today the HCN detection for Cloverleaf @ z=2.56 through 11x magnification

  19. “caustic cosmology” Kneib et al (1996; 2004) Ellis et al (2001) confirm pair at z=5.576 SKA 2004 Penticton, July 20

  20. A2218 z=0.175 (=0.3, =0.7) …targeted groups of multi beams SKA 2004 Penticton, July 20 Artem Tuntsov & Geraint Lewis

  21. A2218 moved to z=1 (=0.3, =0.7) …but it will take a decade to get reliable cluster mass models at z ~ 1 SKA 2004 Penticton, July 20

  22. Depolarization silhouettes • Distant galaxies are too small to be probed by RM grid … but can be probed by Faraday rotation and depolarization of extended background sources e.g. NGC 1310 against Fornax A (Fomalont et al 1989) Polarization from Fornax A (Fomalont et al 1989) “Ant” detected in H (JBH et al. 1995) SKA 2004 Penticton, July 20

  23. Depolarization silhouettes — radio’s own integral field approach New approach to discovery: First identify polarized screens at z  1 Sensitive to H+ along entire column Silhouette gives geometry of absorber Butneed integral field spectrograph to get redshift of H+ Optically bright QSO could be used to identify HI absorbers along same column — great synergy! In survey mode, RM wins out over EM in all three survey dimensions If redshift known, EM wins out! SKA 2004 Penticton, July 20

  24. Closing in on a supermassive black hole …with phase-referenced SKA + VLBI We heard about GR effects at Galactic Center but this will ultimately be possible at 14 Mpc

  25. Closing in on a supermassive BH in NGC 1068 S1: 107 Mo SMBH, x-ray heated torus, FF absorbed radio continuum below 5 GHz C, S2: jet-induced shock structure, C also time variable with H2O maser SKA 2004 Penticton, July 20

  26. Zooming in to S1 …what could we do with SKA + space VLBI !

  27. Precision measurement:Mass of the Local Group and Beyond …of crucial importance to realistic CDM simulations which require FT of Local Group density field

  28. sphere SKA 2004 Penticton, July 20 10 as/yr = 1 km/sec at 20 kpc 10 as = 10% distances at 10 kpc

  29. Era of precision astrophysics • Can register motion of Solar System around Galaxy in just one month (Reid et al 1999)! 220 kms-1 6 mas yr-1 • GAIA will do Galaxy • SKA + VLBI can do Local Group, beyond if can find compact phase reference source, e.g. H2O masers M51: 15 as yr-1 M33: 25-50 as yr-1 IC 10: 25-50as yr-1 … and beyond? SKA 2004 Penticton, July 20

  30. Time Domain

  31. What twinkles in the faint radio sky? • Hard to predict what we might find? Look to optical. • Samples of optically variable or transient sources are massively incomplete at all flux levels, on all time scales from 3 hours to 3 years (Paczynski 2000) • Almost nothing is known about faint variability (V>20) • Microlensing surveys (OGLE, MACHO) reveal great richness even in a few cardinal directions • What might we expect at radio wavelengths? moving, e.g. NEA transient, e.g. GRB, SN, HN, QSO variable, e.g. AGN unexpected, e.g. picolensing, nanolensing, microlensing extremely rare, e.g. shredded star SKA 2004 Penticton, July 20

  32. A case study: Ivezic et al. 2003 SDSS 3 hr3 yr 3,000,000 sources 700 deg2 SKA 2004 Penticton, July 20

  33. Intra-day variability and scintillation • Why do so few active galactic nuclei scintillate? • Intrinsic • Broadened by intervening gas, i.e. behind clusters? We need to identify many more of these, say 1 per sq deg, and then monitor entire sky. • Would we expect to see Faraday screens at greater distances • Galactic Centre, i.e. Galactic wind entrainment • Disk-halo regime

  34. Astrometry Long the domain of radio astronomy but now GAIA inspires us to greater heights! There is a great deal of fundamental science in accurate positions, e.g. Sgr A*, SCUBA identifications, HDF astrometry, NGC 1068 black hole. Fundamental reference frame is at 1 mas (rms) now from 600 QSOs; this is likely to improve by two orders of magnitude or better. Note: “Optical/IR extreme AO” talk of 90dB PSF wing suppression to detect exoplanets; surely a role for radio continuum studies?

  35. Precision MHD • Inhomogeneous fields affect: • Minimum pressure/equipartition estimates (Pacholczyk 1970) • Inverse Compton estimates • Particle aging (Eilek, Melrose, Walker 1997) • Interpreting synchrotron sources (Eilek & Arendt 1996) • Importance of MHD • High sensitivity polarization measurements (<1”) — constant beam size across wavelengths, excellent polarization purity — will be crucial to building realistic MHD models

  36. MHD comes out of the cold In astrophysics, MHD processes abound. They have the potential to be dynamically dominant in most places where observed. • We need a lot of help from theorists…. • Could we expect to see real time behaviour from • small-scale dynamos • astrophysical batteries • ambipolar diffusion… …what is our expectation? Tom Landecker showed us a great deal of polarization structure with no radio EM counterpart, although better match with H EM; what are we looking at?

  37. Spiral galaxy B field (edge on)

  38. Spiral galaxy B field (face on) Fletcher & Beck 2004

  39. Feedback and MHD

  40. Feedback: controlled by nuclear or disk winds? Efstathiou 2000 SKA 2004 Penticton, July 20

  41. Magnetic field in a galactic wind — in the flow or in the halo? Cecil et al (2001) SKA 2004 Penticton, July 20

  42. Entrainment and dragged fields This was quite unexpected — see Cecil et al (2001) — outflow drags field and turn over causing field reversal inside to outside along LOS SKA 2004 Penticton, July 20

  43. Brief summary • SKA holds its head high for observational cosmology • Precision cosmology may come unstuck with GF processes (e.g. w(z) vs. bias evolution) but this is of equal merit! • SKA has maybe the biggest potential for future physics • study of compact sources • MHD: far more theoretical work required here— the people exist • How to ensure survival of science case until 2020? • Complexity is good: crucial weak signal against complex background • Precision measurement is good: astrometry, proper motions, water maser kinematics, polarization • Time domain should be a winner! • Concept of multi beams means that a few can be focussed on integrations of many months or years in order to reach syst. limit • Decide soon-ish on science case; stick with a few key technologies; develop design reference mission; then let engineers do their job!

  44. Sound bites and science lobby Seeing back to before the first stars and black holes Reaching down to the magnetized cosmic web Discovering the source of the cosmic magnetic field Observing the most energetic sources in the Universe i.e. jets in clusters, and cluster-cluster collisions Picture shown here from Nulsen et al. (2004) > 1061 erg

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