Square Kilometre Array
John Conway
Onsala Space Observatory, 18 June 2012 Radio Observations for Astronomy
• Astrophysics today requires ‘pan-spectral’ data – but radio provides unique information.
• ‘Radio’ astronomy one of two EM windows visible from Earth’s surface.
• Encompasses 10 MHz – 1 THz 5 (factor of 10 in frequency, needs multiple technologies!). The optical/IR window covers just over factor of 30.
• Radio unique properties- Obscuration independent - high angular resolution (1mas) – unique lines – magnetic fields. Radio Telescope Sensitivity Evolution
Sensitivity improves 107 in 80 yrs(collecting area, receivers and Bandwidth)
Groet Reber’s Backyard SKA (2020+)- 40 telescope (1940) times EVLA Today’s State of Art
• To get high resolution need interferometers, resolution inversely proportional to longest baseline - large single dishes (i.e Arecibo) less important cm-wave mm-wave
EVLA (Jansky Very Large Array) – Atacama Large Millimetre Array refurbished VLA, New Mexico USA (ALMA) – 5000m altitude Chile. 20 – 27 x 25m diameter dishes dishes now soon 66 dishes of 12m 300MHz – 50GHz diameter – 90GHz – 800 GHz FUTURE RADIO TELESCOPES 2012 2013 2014 2015 2016 2017 2018 2019 2020 m -wave LOFAR (NL/ Europe)
MeerKAT (S.Africa) Jansky VLA
Square Kilometre Array – cm -wave SKA (S. Africa and Australia/NZ) – (cm) 50 times EVLA (m) 10 times LOFAR ASKAP(Australia)
ALMA mm -wave (Chile) Great Observatories for the coming decades
ALMA mm/ sub-mm E-ELT optical
SKA JWST infra-red radio
IXO Xray Top-level description
• Construction will proceed in two phases: SKA1, SKA2 SKA1 will be a subset (~10%) of SKA2 70 MHz – 3GHz 100 km baselines Major science observations already possible with SKA1 in 2020
Phased construction allows maximum use of advances in technology SKA1 baseline design Baseline technologies are mature and demonstrated in 250 Dishes the SKA Precursors and Pathfinders Central Region
Single pixel 50 Sparse feed Aperture Arrays Artist renditions from Swinburne Astronomy Productions SKA2 including Advanced technologies
250 Dense 2500 Dishes Aperture Arrays 3-Core Central Region
250 Sparse Aperture Arrays
Artist renditions from Swinburne Astronomy Productions SKA2
SKA2
SKA1 EVLA LOFAR SKA2
SKA1
LOFAR
EVLA SKA2 Key Science Drivers
ORIGINS Neutral hydrogen in the universe from the Epoch of Re-ionisation to now When did the first stars and galaxies form? How did galaxies evolve? Dark Energy, Dark Matter Astro-biology
FUNDAMENTAL FORCES Pulsars, General Relativity & gravitational waves Science with the Origin & evolution of cosmic magnetism Square Kilometre Array (2004, eds. C. Carilli & S. Rawlings, New TRANSIENTS (NEW PHENOMENA) Astron. Rev., 48) Epoch of Reionization z = 9.8 z = 12.1 Universe made rapid transition from largely neutral to largely
ionized (zion ~ 6–11)
SKA objective: Image the IGM transition in the H I (21-cm) line
• Also HI abs to ly-alpha absorbers, galaxies with Gunn- Peterson trough. • Possible trace HI to higher z than EoR in absorption EoR Timeline EoR science goals
Absorption studies up to z=25 if there are continuum sources >1mJy – first accreting black hole OR PopIII supermovae Galaxy Evolution back to z~10?
HDF VLA
~ 3000 galaxies ~15 radio sources HDF SKA
8 hr SKA continuum observations at 1.4GHz 10nJy/beam noise 2700 sources – note only 2.5 x 2.5 arcmin shown (HDF field size. =100 pointing 90GHz ALMA mosaic) - SKA instantaneous FOV at least 1 x 1deg hence 1million sources per pointing (!) Galaxy Assembly & Evolution H I is the raw material for galaxies and star formation • How do galaxies turn gas into stars?
• Detect 109 galaxies in HI ) -1 • Measure in resolved sources
Gravitational and atomic mass dex • How does gas content vary with -3 – Morphology; (Mpc
– Redshift; φ – Environment; log – Mergers; – Feedback 8 10 log M Baryon Acoustic Oscillations
Remnant of plasma acoustic WMAP oscillations in early Universe (z ~ 1100)
• DA(z) = angular size distance as a function of redshift • ~ 100 h-1 Mpc “standard ruler” • Measures expansion rate of Universe • Constrain equation of state of dark energy • Euclid – (Saturday’s talks) a competitor. SDSS (z ~ 0.35) SKA: BAOs
• Next-generation goal: Z~1.5 – Survey large volume – Slice into redshift bins – Detect BAOs in each z bin
• SDSS surveyed ~ 1 Gpc3 SDSS One redshift bin ~ 0.35 • SKA targeting 100 Gpc3 (z >~1.5) • A billion H I galaxies SKA SDSS – Intrinsically spectroscopic survey – Different biases than LSST, Euclid/WFIRST Local HI in universe
Atomic masses, dark matter masses, connection to ‘cosmic web’ feeding SF in galaxies Pulsars – Testing GR and Detecting Gravitational waves
• “Interesting” pulsars < 1% of population – Rapidly spinning millisecond pulsars – Ultra-relativistic binaries – Ultra-stable millisecond pulsars • Find only the most interesting by finding all pulsars in galaxy (approx 10,000)! Pulsar GR measurements
• Do timing observations of pulsar-stellar BH and pulsar-SgrA* to test GR in strong field limit.
• Measure decay of orbit from GravWaves – measure BH mass, Spin and quadropole moment
• ‘No hair’ theorem of GR - spin and quadrapole effects related.
• Test mechanical properties of neutron star – distortion in elliptical orbit –properties of nuclear matter.
• Accurate measurments of above require accurate distances possible by pulsar astrometry. SKA: Gravitational Wave Detector ) Ω log (
Test masses on lever arm • Pulsar Timing Array = freely-falling millisecond pulsars • LIGO = suspended mirrors log (f/Hz) • LISA = freely-falling masses in spacecraft • Detect SMBH mergers – and cosmological origins – topology defects etc.
Cosmic Magnetism
1) Origin of B fields in Galaxies
-Primordial field -T urbulent dynamo -M ean field alpha-Omega
Predict different field configs in galaxies
2) Synchrotron or limits in first galaxies ‒ direct limit on B-fields and cosmic evolution.
3) Try to measure the IGM field strength The Dynamic Radio Sky
• Neutron stars • GRBs (g-ray loud; g-ray
– Magnetars quiet?) Amplitude
– Giant pulses – Afterglows – Prompt emission? – Short GRBs? • Sub-stellar objects – Brown dwarfs – Extrasolar planets? Frequency(MHz) Rotating Radio Time • Microquasars Transients (RRATS) • Scintillation • UHECRs • ETI • Exploding black holes • ???
Pulsating Brown Dwarfs Radio Supernova detection rate
Lien et al (2011) estimate of core-collapse rate and z distribution (red 50nJy limit) - total 620 events per year per deg2 independent check of SFR of universe – crude z from rise time luminosity relations, Science summary
Epoch of Re-Ionisation SKA: IGM and First Galaxies
Galaxy Assembly & Evolution SKA: black holes, atomic gas, star formation, feedback
Astrobiology SKA: proto-planetary disks, molecules, planets, SETI
Baryonic Acoustic Oscillations SKA: H I BAOs (“Billion-Galaxy Survey”)
Fundamental forces SKA: magnetic fields, gravitational waves, strong field gravity Swedish Involvement
-- LOFAR-Sweden has 63 members ‒ very active members in EoR, Magnetism, Surveys and Solar Physics and Space weather (magnetism KSP next week at Onsala), Surveys
- Headquarters of SKA organisation in Jodrell Bank, UK. New buiding ready by end of 2012, design staff.
-Sweden filling in forms to join next pre-constriction phase (2012-2016) of SKA- join UK,NL,Italy, (soon Germany), SA, Australia, New Zeeland, Canada, China.
-At Onsala developing wide band feed technology, calibration methods, dish choices etc.
-- decision to fund phase 1 will be in 2014 approx, cost 350MEuro ‒ phase 2 construction later (2018?) cost 1.5 billion Euro. ‒ similar to E-ELT.