The Square Kilometer Array

Transcription

1 The Square Kilometer Array Jim Cordes, Cornell University For the International SKA Project and the U.S. SKA Consortium 13 June 2007 Presentation to the Committee The Square Kilometer Array Program The SKA Project Early 90s: the Hydrogen telescope Evolved science case International project from the start 17 countries, 1/3 US participation SKA science case 1990s Taylor & Braun SWG of International SKA Project Fundamental questions in physics, astrophysics and astrobiology Unprecedented capacity for discovery Specifications and Technology Array with increase in sensitivity over existing telescopes (~ 1 km 2 /40 K) Frequency range: GHz (nominal) ( GHz) Innovative design needed to reduce cost 1,000/meter 2 vs. 10,000/meter 2 Cost cap ~ 1.5 billion (likely) Implementation Timeline: phased deployment Siting: two acceptable sites (RSA, WA) for low/mid freq. high frequencies: US site possible Technology development/pathfinders Science pathfinders SKA as a Radio Synoptic Survey Telescope (RSST) Reference Design: LNSD + phased arrays Memo 69 Science Specifications: Memo

2 Questions that the SKA can address Fundamental Physics What is dark energy? What is dark matter? Did Einstein have the last word on Gravity? How do cosmic accelerators work and what are they accelerating? What are the new states of matter at exceedingly high density and temperature? Is a new theory of light and matter needed at the highest energies? Complexity in the Universe How does a simple big bang turn into a universe with stars, planets and life? How do planetary systems form? How common are planetary systems? What is the role of interstellar molecules in jump starting life on planets? Is intelligent technological life common or rare? Science with the SKA 2

3 The Program of SKA Science International Science Working Group Full science case published in New Astronomy Reviews, Vol 48, 2004 Carilli and Rawlings, editors Five Key Science Projects: 1. Probing the Dark Ages 2. Galaxy Evolution, Cosmology and Dark Energy 3. The Origin & Evolution of Cosmic Magnetism 4. Strong Field Tests of Gravity Using Pulsars and Black Holes 5. The Cradle of Life + The Exploration of the Unknown: design to maximize discovery Five Key Science Areas for the SKA Topic Probing the Dark Ages Gravity: Pulsars & Black Holes Cosmic Structure & Evolution Goals 1. Map out structure formation using HI from the era of reionization (6 < z < 13 20?) 2. Probe early star formation using high-z CO 3. Detect the first active galactic nuclei 1. Precision timing of pulsars to test theories of gravity approaching the strong-field limit (NS-NS, NS-BH binaries, incl Sgr A*) 2. Millisecond pulsar timing array for detecting long-wavelength gravitational waves 1. Understand dark energy [equation of state, w(z)=p/ρ] 2. Understand structure formation and galaxy evolution 3. Map and understand dark matter Cosmic Magnetism The Cradle of Life Determine the structure and origins of cosmic magnetic fields (in galaxies and in the intergalactic medium) vs. redshift z 1. Understand the formation of Earth-like planets 2. Understand the chemistry of organic molecules and their roles in planet formation and generation of life 3. Detect signals from ET 3

4 Flowdown from SKA Science to Technical Requirements Topic Dark Energy & Cosmic Structure Gravity: Pulsars & Black Holes Probing the Dark Ages Cosmic Magnetism The Cradle of Life Type of Obs. M * galaxies at z=2 Full Galactic Census Precision Timing Extragalactic pulsars HI structure 6 < z < 13 CO at z>6 The first AGNs Faraday rotation of 10 8 extragalactic sources protoplanetary disks SETI Freq. (GHz) GHz ( ) >20 All 300 km 100 to > Baselines Core < few km Extended >3000 km > 3000 Special Requirements Large FOV for survey speed Full SKA for extragalactic; Full FOV fast sampling to 35 GHz for CO -40dB polarization purity Multiple beams Exploration of the Unknown Unplanned discoveries Pulsars Microwave Background Cosmic Evolution Dark Matter in galaxies Quasars Jets + Superluminal motion SKA Discovery Potential 10 4 x existing radio telescopes NRC Spectrum Study 4

5 (2007 Jan) Implementation of the SKA Three frequency bands: Low: 100 to 300 MHz Epoch of Reionization, high-z radio galaxies, transients, SETI Mid: 0.3 to ~ 3 GHz High-z hydrogen, pulsars, transients magnetic fields, SETI High: ~3 to ~ 25 GHz High-z CO, astrobiology, protoplanetary disks, Galactic center pulsars, SETI Technologies: Low frequencies: dipole arrays Mid/Low: aperture arrays (phased arrays looking up) Mid/High: large-n array of small dishes (LNSD concept) + smart feeds (phased array feeds, 10:1 broadband feeds) 5

6 Technology Trends for the SKA: LNSD + aperture arrays Receivers on a chip Wide field-of-view radio cameras Data-adaptive interference nulling, mitigation, and excision Real-time VLBI (long-haul signal transport) Very long integration times at high sensitivity required for some SKA science (100s of hours) Mass production SKA Frequencies and Technologies Frequency Ranges for Key SKA Science Dark Ages EoR/HI First AGNs CO Gravity Cosmic Structure Galactic High-z L* galaxies weak lensing Sgr A* pulsars Cosmic Magnetism Cradle of Life Dipoles Faraday Rotation Paraboloids, Aperture Arrays molecules protoplanetary disks SETI Paraboloids 0.1 GHz 1 GHz 10 GHz 6

7 SKA Frequencies and Technologies Frequency Ranges for Key SKA Science Dark Ages EoR/HI First AGNs CO Gravity Cosmic Structure Galactic High-z L* galaxies weak lensing Sgr A* pulsars Cosmic Magnetism Cradle of Life Dipoles Faraday Rotation Paraboloids, Aperture Arrays molecules protoplanetary disks SETI Paraboloids 0.1 GHz 1 GHz 10 GHz Dark Ages Gravity Cosmic Structure Cosmic Magnetism Cradle of Life SKA Frequencies and Technologies Low-f Pathfinders: EoR experiments Transient detection LOFAR (Netherlands) MWA/LFD (US/Aus) PAST (China) LWA (US) EoR/HI Dipoles Frequency Ranges for Key SKA Science Galactic High-z L* galaxies First AGNs 0.1 GHz 1 GHz 10 GHz CO High-z CO, ppds, weak lensing Faraday Rotation Mid-f Pathfinders: High-z HI, pulsars, molecules Faraday rotation Arecibo, GBT, ATA Paraboloids, ASKAP/Miranda(Aus) Aperture Arrays MeerKAT (South Africa) EMBRACE (Europe) High-f Pathfinders: GC Sgr pulsars A* pulsars GBT, EVLA,ATA, ALMA protoplanetary disks SETI Paraboloids 7

8 Reference Design Reference Design Memo 69 8

9 Site selection Physical characteristics required: Very quiet radio frequency environment, particularly for the core region Large physical extent (>3000 km) Low ionospheric turbulence < 3 GHz Low troposphere turbulence > 8 GHz Two acceptable sites: RSA, WA Decision expected in Expected to apply for low-f/mid-f arrays High-f site may be in the U.S. (extension of EVLA+VLBA) Long-Wavelength Array (LWA) sited in U.S. Southwest (SW Consortium) Sydney: population 4 million Narrabri: population 4000 Mileura: population 4 Results of LWA Radio Interference testing at Twin Peaks site 9

10 Australia + New Zealand South Africa + 7 countries 10

11 MeerKAT Timeline ATA 10% SKA Phase I LOFAR MWA/LFD MIRA ASKAP Full SKA LWA Now ATA MeerKAT LOFAR Size MIRA/ASKAP SKA Phase I Full SKA 100-m class Arecibo class SKA 11

12 SKA Program Plan A personal take on what should be proposed to the Decadal Survey EoR Array: < 0.3 GHz Science goal: detection and imaging of EoR Array optimized for this goal, separable from (the rest of) the SKA Context: Informed by LOFAR, MWA, PAPER (detection!) Expand later as imaging array contingent on results from current arrays Substantial U.S. contribution next decade Radio Synoptic Survey Telescope: GHz (higher desirable) Survey oriented: Dark Energy, Gravity/Pulsars, Transients, Magnetism, Relativistic objects Consistent with Reference Design but needs technology decisions and optimization U.S. a significant partner with specific deliverables consistent with funding and time line (E.g., antenna/feed designs, processing algorithms, backends) High-frequency Array: 1 25 GHz Science goals: Imaging protoplanetary disks, high-z CO, SETI; Follow-on to EVLA, ALMA; complementary to JWST, TPF, etc. Consistent with Reference Design Siting re-evaluated based on characteristics of RSST array site Substantial U.S. contribution Deferred construction 13 June 2007 Jim Cordes, Cornell University The History of Hydrogen COSMIC HISTORY OF THE UNIVERSE Ionized H (p + e-) Neutral H ( recombination ) redshift z ~ 1200 Reionization from the first stars and galaxies: z ~ 15 to 6 redshifted hydrogen frequency: f = 1.42 GHz / (1+z) = MHz Galaxy evolution and acceleration of the universe: z ~ 2 to 0 redshifted hydrogen frequency: f = 1.42 GHz / (1+z) = GHz Present day (z = 0) rest frequencies: H 1.42 GHz 22.2 GHz H2O CO GHz D. Djorgovski 13 June 2007 Jim Cordes, Cornell University 12

13 Probing Reionization with the 21 cm Line 6 z MHz ν 60 MHz Furlanetto et al Global reionization signature in radio spectrum Minihalos, protogalaxies and AGN HII regions Tomography: δtb(θ,ν) Gnedin & Ostriker 1997 Non-Gaussian fluctuations (bispectrum) Cosmic D/H ratio using H fluctuations as template for D Absorption against the first AGNs (21-cm forest) N. Gnedin Carilli, Gnedin & Owen June 2007 Jim Cordes, Cornell University Probing the Dark Ages COSMIC HISTORY OF THE UNIVERSE Challenges Widefield imaging at low frequencies (ionosphere) Galactic foregrounds (polarized synchrotron) Point source removal Radio Frequency Interference June 2007 Jim Cordes, Cornell University 13

14 The Nature of Dark Energy SKA Role Dark Energy Task Force: SKA=Stage IV experiment The Composition of the Universe 1. Locate and measure 3D spatial distribution of 10 9 galaxies via their hydrogen emission: d θ (z), H(z) 0.45 to 1.4 GHz 2. Large-scale weak lensing survey: d θ (z), structure formation ~1.4 to 5 GHz Detect Baryon acoustic oscillations to high precision (w to a few %) Dark Energy Task Force Recommendations The dark energy program should have as its goals to: Determine whether the accelerating expansion is consistent with a cosmological constant Measure any time evolution of the dark energy Search for possible failures of GR (e.g. cosmic expansion vs. structure formation) No single technique can answer the outstanding questions about dark energy. Because JDEM, LST and SKA all offer promising avenues to greatly improved understanding of dark energy, we recommend continued research and development investments to optimize the programs and to address remaining technical questions and systematic-error risks. We recommend that the community and the funding agencies develop a coherent program of experiments designed to meet the goals and criteria set out in these recommendations. 14

15 Was Einstein Right About Gravity? The SKA as a Pulsar/Gravity Machine Relativistic binaries (NS-NS, NS-BH) for probing strongfield gravity Orbit evolution + propagation effects of pulsars near Sgr A* Millisecond pulsars < 1.5 ms (EOS) MSPs suitable for gravitational wave detection 100s of NS masses (vs. evolutionary path, EOS, etc) Galactic tomography of electron density and magnetic field; definition of Milky Way s spiral structure Target classes for multiwavelength and non-em studies (future gamma-ray missions, gravitational wave detectors) Millisecond Pulsars Today Future Relativistic Binaries Today Future SKA SKA only 9! Blue points: SKA simulation Yellow points: known pulsars ~10 4 pulsar detections First Double Pulsar: J Lyne et al.(2004) P b =2.4 hrs, dω/dt=17 deg/yr M A =1.337(5)M, M B =1.250(5)M obs 13 June 2007 Now to 0.05% Jim Cordes, Cornell University exp Testing GR: s s = ± Kramer et al.(2004) 15

16 Galactic Center Region Sgr A* = black hole with a surrounding star cluster with ~ 10 8 stars. Many of these are neutron stars. 327 MHz VLA image Detecting pulsars near Sgr A* is difficult because of the intense scattering screen in front of Sgr A*. Multipath differential arrival times τ d ~ 2000 ν -4 sec Solution: high sensitivity at high frequency 16

17 Pulsars as Gravitational Wave Detectors Gravitational wave background pulsar pulses Gravitational wave background Earth The largest contribution to arrival times is on the time scale of the total data span length (~20 years for best cases) Pulsars as gravitational wave detectors: Earth and pulsar = test masses Requires sub-μs TOAs ~ 10-9 Hz gravitational waves Complementary to LIGO II and LISA 17

18 Differential rotation, superfluid vortices Glitches Spin noise Emission region: beaming and motion Interstellar dispersion and scattering Uncertainties in planetary ephemerides and propagation in interplanetary medium GPS time transfer Additive noise Instrumental polarization Radio Aspects of the Transient Universe Time domain science: the transient sky = frontier for all wavelengths Less so at high energies BATSE, RXTE/ASM, Beppo/Sax, SWIFT, etc. More so for optical, radio LSST (LST) = Large Optical Synoptic Survey Telescope RSST = Radio Synoptic Survey Telescope Do SKA Key Science + discovery science in parallel Dark energy, galaxy evolution, pulsars/gravity, magnetism, transients 18

19 Phase Space for Transients: RRATs (McLaughlin et al. 2006) S pk D 2 vs. νw Time series of the radio emission detected with the VLA from the M9 dwarf TVLM Every hours a periodic pulse is detected when extremely bright, beams of radiation originating at the poles sweep Earth when the dwarf rotates. Artist's impression of a brown dwarf with "super-aurorae" at its magnetic poles, causing the pulsed radio emission. (Credit: Copyright National University of Ireland, Armagh Observatory, National Radio Astronomy Observatory, United States Naval Observatory & Vatican Observatory, Arizona) W = pulse width or characteristic time scale Transient Signals: Filling phase space with hypothetical new discoveries: Prompt Gamma-ray emission Evaporating black holes Maximal giant pulse emission from pulsars ETI s asteriod radar What else? 19

20 SKA Science Before the SKA Epoch of Reionization: Detection experiments in the Netherlands and Australia (LOFAR, MWA) Dark Energy (billion galaxy survey): Define the low redshift universe, hydrogen mass distribution in galaxies Arecibo deep surveys using ALFA and follow-on system ( GHz) Pulsars: Strive for full Galactic census (including GCs and GC): Arecibo ALFA, GBT, EVLA Pulsar timing array: roadmap from now to the SKA Techniques for improving timing precision Faraday rotation measure studies Transients: Monitor the sky as much as possible with flexible analysis of the timefrequency plane Solid angle + t-f analysis more important at this stage than sensitivity Explore cross-wavelength synergies RFI Excision: Continuous development using single-dish and array systems Pulsar Survey with Arecibo Multibeam System (ALFA) (Arecibo will provide the most sensitive pulsar surveys until a 10% SKA comes on line) Detection of a strong pulsar amid RFI Detection of a weak millisecond pulsar in beam 1 20

21 Context: Responds to current international context for the SKA: Acceptable sites identified Reference design exists Pathfinders underway A four-year project that will provide input to the SKA design and to the U.S. Decadal Survey Primary work areas: 1.Antennas with single-pixel broadband feeds and receivers 2. Signal transport and processing; RFI excision; synoptic survey design and data management 3. Cost studies 4. System design Collaborations: European Framework 7 SKA Design Project (May 2007) DSN array (70m equivalent) w/ 12m dishes Status and Recent Developments NSF will fund the U.S. SKA TDP at $12M for four years EC response to European FP7 project expected mid-2007 South African MeerKAT funded at 100M Australian ASKAP (MIRA) funded at A$100M (as of 8 May 2007) Preparations for the U.S. Decadal Survey ( ): Chicago III meeting to define U.S. science priorities that require new m/cm telescopes Associated Universities, Inc. (AUI)-sponsored preparation for the decadal survey (m, cm, mm) Strong interest in EVLA/VLBA buildout to cover high-frequency science; needs to be reconciled with international SKA project Possible scenario for high frequencies in the U.S.» Technology development proposed to decadal survey» Addition of modest collecting area to EVLA/VLBA in the next decade (to 2020)» Proposal to the ~2019 decadal survey for large-scale construction 21

22 Ending Points The SKA is an ambitious, revolutionary project for tackling fundamental questions in physics, astrophysics and astrobiology The SKA is likely to be built in three bands with phased construction over the next 15 years SKA-low SKA-mid <100 MHz to 300 MHz 0.3 to 3 GHz (or higher) SKA-high 1 to 25 GHz (or higher) extend EVLA? SKA-mid can operate as a Radio Synoptic Survey Telescope that does a billion-galaxy survey while also doing gravity/pulsars, magnetic fields and transient science Building the SKA is a challenge in technology development, in funding and in international collaboration Initial arrays will begin construction this decade while full deployment will take until at least

23 Extra Slides SKA Candidate Decade-Bandwidth Feeds for the SKA 23

24 Figure of Merit for Radio Survey Capabilities Courtesy of C. Blake 24

25 Blind Surveys with SKA Number of pixels needed to cover FOV: N pix ~(b max /D) 2 ~10 4 Number of operations to form beams N ops ~ petaop/s Post processing per beam: Single-pulse and periodicity analysis Dedisperse (~1024 trial DM values) FFT + harmonic sum Orbital searches (acceleration ++) RFI excision Correlation is more efficient than direct beam formation Requires signal transport of individual antennas to correlator Post processing ~ 10% of beam forming 10 4 beams needed for full-fov sampling Extra Slides Discovery 25

26 Key Discoveries that Illustrate Discovery Space in Radio Astronomy Discovery Date Enabled by Telescope Cosmic radio emission 1933 ν Bruce Array (Jansky) Non-thermal radio emission 1940 ν Reber antenna Solar radio bursts 1942 ν, Δt Radar antennas Extragalactic radio sources 1949 Δθ Australia cliff interferometer 21 cm line of hydrogen 1951 theory, Δν Harvard horn antenna Mercury and Venus spin rates 1962, 1965 Radar Arecibo Quasars 1962 Δθ Parkes occultation Cosmic Microwave Background 1963 ΔS, calibration Bell Labs horn Confirmation of General Rel. 1964, 1970s theory, radar, Δt, Δθ Arecibo, Goldstone, VLA,VLBI Cosmic masers 1965 Δν UC Berkeley, Haystack Pulsars 1967 Ω, Δt Cambridge 1.8 hectare array Superluminal motions in AGNs 1970 Δθ Haystack-Goldstone VLBI Intersteller molecules and GMCs 1970s theory, ν,δν NRAO 36ft Binary neutron stars and gwaves 1974-present Ω, Δt Arecibo Gravitational lenses 1979 theory, Δθ Jodrell Bank interferometer First extrasolar planet system 1991 Ω, Δt Arecibo Size of GRB fireball 1997 λλ, ΔS, theory VLA Solar radio bursts Quasars Cosmic masers Pulsars Gravitational lenses Size of GRB fireball Nobel Prizes from the Discovery Space in Radio Astronomy Discovery Cosmic radio emission Non-thermal radio emission Extragalactic radio sources 21 cm line of hydrogen Mercury and Venus spin rates Cosmic Microwave Background Confirmation of General Rel. Superluminal motions in AGNs Intersteller molecules and GMCs Binary neutron stars and gwaves First extrasolar planet system s 1974-present Date 1962, , 1970s ν ν ν, Δt Δθ theory, Δν Radar Δθ ΔS, calibration theory, radar, Δt, Δθ Δν Ω, Δt Δθ theory, ν,δν Ω, Δt theory, Δθ Ω, Δt Enabled by λλ, ΔS, theory Bruce Array (Jansky) Reber antenna Radar antennas Australia cliff interferometer Harvard horn antenna Arecibo Parkes occultation Bell Labs horn Arecibo, Goldstone, VLA,VLBI UC Berkeley, Haystack Cambridge 1.8 hectare array Haystack-Goldstone VLBI NRAO 36ft Arecibo Jodrell Bank interferometer Arecibo VLA Telescope 26

27 Extra Slides Dark Energy Baryonic wiggles throw light on dark energy 10% SKA/LSST may see subtle deviations from a cosmological constant explanation for dark energy SKA + Planck get standard rod to high enough precision to push to 1% accuracy on w 27

28 Features of SKA as a Stage IV Dark Energy Enterprise DETF: The combination of high-precision redshift information with stable interferometric imaging can produce BAO and WL data that is unsurpassed in statistical and systematic quality, over the volume that is accessible to the SKA. Billion-galaxy survey in HI (z max ~2): 50 to 70% sky coverage High survey speed with FoV = 10s of deg 2 Get redshifts automatically W parameters (2D) to a few percent Weak lensing: Widefield survey, redshifts automatic, as above PSF well known, ionospheric effects calibratible Requirements: 0.4 to 1.4 GHz Resolve galaxies baselines up to 300 km Wide FoV: very small dishes + single pixel feeds larger dishes with phased-array feeds Issues: Drives sensitivity specification of the mid-frequency SKA Electronics and signal-processing costs for very small dishes Achieving low system temperature with phased-array feeds Requires a large fraction of array time for 1 to 5 years 28

29 Extra Slides Pulsars M. Kramer 29

30 Frequency P Time Interstellar Scintillation RFI Astrophysical effects are typically buried in noise and RFI 30

31 How Good are Pulsars as Clocks? MSP J P=3 ms + WD Jacoby et al. (2005) Weighted σ TOA = 74 ns Shapiro delay 31