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Scientific Motivation�for�Deep Field Imaging with the SKA

S.A. Torchinsky�Observatoire de Paris�SKADS Project Scientist

S.A. Torchinsky (1 of 1051920)

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Scientific Motivation for Imaging with SKA

Cambridge, 25 August 2008

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Motivational Outline

  • Some definitions
  • SKA Key Science questions
    • Cradle of Life
    • Tests of Gravity
    • Cosmic Magnetism
    • Probing the Dark Ages
    • Large Scale Structure
    • Transients
  • SKA in operation

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Scientific Motivation for Imaging with SKA

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Some Definitions

Deep Field Imaging with the SKA

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What is “Deep Field” ?

  • The SKA will be ~10x more sensitive than any current radio telescope. Compared to current instruments, everything done by SKA is “deep field”

Answer: Everything

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What is “Imaging” ?

  • Spatial (angular) information
  • The SKA will have aperture plane arrays forming multiple beams on the sky (low to mid frequencies).
  • The SKA will also have (almost certainly) multibeam receivers in dishes for the higher frequencies.
  • All SKA observations will give spatial information.

Answer: Everything

Tony Willis will give a more technical definition of imaging later today

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What is the “SKA” ?

  • 70MHz to 25GHz
  • Exquisite angular resolution (~10mas @ ~1GHz)
  • Simultaneous wide field
  • Extremely sensitive
  • High dynamic range
  • Fast time constant

Answer: The Be All End All

Paul Alexander will sum up with “Road to SKA”

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What is “Scientific Motivation” ?

  • What questions do we want to answer?
  • Why do we want to answer those questions?
    • ie. How do they relate to bigger issues (the Big Picture)

Topic for pub discussion…

Why do we want to understand the Big Picture?

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Scientific Motivation for Imaging with SKA

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Is there a Big Picture?

(topic for the second round)

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Scientific Motivation for Imaging with SKA

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Scientific Motivation

Tests of gravity

Epoch of Reionisation

Cosmic Magnetism

Cradle of Life

Large Scale Structure

Transient Universe

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Scientific Motivation for Imaging with SKA

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SKA Science Book

Chris Carilli & Steve Rawlings,

New Astronomy Reviews, Vol.48, Elsevier, Dec. 2004

​

http://www.skads-eu.org/p/SKA_SciBook.php

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Cosmology, Galaxy Formation

and Astroparticle Physics on

the Pathway to the SKA

Hans-Rainer Klöckner, Steve Rawlings,

Matt Jarvis, Angela Taylor (eds.)

Cosmology, Galaxy Formation and Astroparticle Physics on the Pathway to the SKA

Available online:

www.skads-eu.org (click “memos” or “documents”)

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Scientific Motivation for Imaging with SKA

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Cradle of Life

What conditions are necessary for the development of life?

How are planetary systems formed?

Is the solar system a special case?

How and where are complex (organic) molecules formed?

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Scientific Motivation for Imaging with SKA

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Cradle of Life

  • Protoplanetary disks resolved to Earth-like orbits
  • Organic molecules
    • methanol (834 MHz)
    • acetaldehyde (1.1 GHz)
    • acetamide (9.2 GHz)
    • cyclopropenone (9.3 GHz)
    • propenal (26 GHz)
  • Extrasolar planets

G. Bryden / NASA

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Scientific Motivation for Imaging with SKA

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Cradle of Life

Is there anybody out there?

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Scientific Motivation for Imaging with SKA

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Indicators of �Extra Terrestrial Intelligence

Project

Phoenix

Allen

Telescope

Array

SKA

Jill Tarter

SETI at leakage levels from nearby stars

eg:

  • planetary radar
  • Interplanetary communication
  • Interstellar communication

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Scientific Motivation for Imaging with SKA

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Cradle of Life

More on star formation and stellar environments from Phil Diamond on Wednesday

More on planet formation and organic molecules from John Richer on Thursday

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Scientific Motivation for Imaging with SKA

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Strong Field Tests of Gravity

Is Einstein right about gravity?

Is there a strong-field limit at which GR is no longer the correct description of gravity?

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Strong Field Tests of Gravity

Binary orbit permits determination of masses

Relativistic effects permit (re) determination of masses.

ALL MUST AGREE

http://www.jb.man.ac.uk/~pulsar/

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Strong Field Tests of Gravity

  • Large surveys will find exotic binarys
    • ~20 000 pulsars in the galaxy
    • Nearly edge-on Pulsar – Black-hole binary (at least one)
      • Probe eg. Frame dragging, cosmic censorship, no hair theorem

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Pulsar Timing Array

Is there a gravitational wave background? Is it primordial?

Can we probe the Universe at times before the Epoch of Recombination when the Universe was opaque to EM radiation?

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Pulsars in Globular Clusters

Freire et al 2003

Pulsar positions in Tuc47

Is this imaging?

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What is “Imaging” ?

  • Spatial (angular) information

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Pulsars in Globular Clusters

Freire et al 2003

Pulsar positions in Tuc47

Is this imaging?

Yes.

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Timing known pulsars

Parkes Beam!

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Pulsar positions from timing

  • Pulsar with known period and period derivative can be localised by the variations in the pulse time-of-arrival
  • Earth orbit around the sun affects the time-of-arrival
  • also for pulsar binary orbits
  • These effects can be separated, giving a high precision to the pulsar position

Pulsar timing proves that the Earth orbits the Sun

Freire, personal communication

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Imaging pulsar positions

  • In principle, the SKA can do timing measurements of the whole visible sky, and simultaneously get timing results and positions of all the detected pulsars (with a bit of a trade-off on sensitivity)
  • In practice, it will take a lot of computing power and data transfer!

more on pulsars by Tony Hewish

on Wednesday.

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Interlude

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The History of the Universe

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Cosmic Microwave Background

How precisely can we know the fundamental parameters of the Universe?

More on CMB imaging by Anna Scaife on Tuesday

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Probing the Dark Ages

When did the first luminous objects form? When was “first light”?

How did they form, and over what period of time?

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Epoch of Reionisation

SKA will detect the Epoch of Reionisation and map the evolution history of the first luminous objects

Di Matteo et al

More from Ger de Bruyn on EoR with LOFAR on Tuesday

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Cosmic Magnetism

  • Were they always there? (primordial)
  • Were they generated over the evolution of the Universe? (dynamo)

M 51 VLA+Eff 6cm

(Fletcher & Beck)

What is the origin of magnetic fields in the Universe?

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Cosmic Magnetism

SKA will measure Faraday rotation of > 107 polarised background sources

​

NGC 891 (Krause)

More from�Paul Alexander on Wednesday

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Dark Energy

What is the nature of Dark Energy?

Is it just a geometrical feature of General Relativity?�(was Einstein wrong when he thought he was wrong?)

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Large Scale Structure

Billions of galaxies!

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Baryonic Acoustic Oscillations

  • Improve signal confidence by measuring wiggles in separate redshift bins
  • A catalog of a billion galaxies
  • Position and redshift measured simultaneously
  • There are fluctuations at all scales but there is a preferred scale of around 1 deg.

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Complementarity with Planck

1%

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HI in Galaxies

More on HI galaxy surveys from Filipe Abdalla on Thursday

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Dark Mass

Where is the dark mass in the Universe?

How is it distributed?

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Cosmic Shear

  • Integrated gravitational lensing along line-of-sight
    • “weak lensing”
  • Requires large statistics
    • SKA continuum survey of 10 Billion galaxies
    • Clean sample
      • Reject star burst galaxies which may be the result of mergers�(morphological alignment not the result of cosmic shear)
      • Still have a large sample with SKA
    • Improve result with analysis in redshift bins
      • Redshifts from SKA HI survey

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Imaging Galaxies

More from Elias Brinks, Scott Chapman, and other short talks on Thursday

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The Expansion of the Universe

What is the precise value of H0?

1929

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Measurement of H0 �with water masers

Case of NGC 4258:

(Greenhill et al, 1995,�Aragon et al 2007)

​

Water masers at various z

will provide H0 with 1% precision

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Proper motions of Water Masers

50 masers known today

(mainly GBT data)

​

For NGC 4258: 3%

precision (proper motions

over 6 yrs with VLBI)

​

SKA will find ~1000 masers

​

With ~10% useful for proper motion

100 masers

🡺 1% on H0

Greenhill 2004

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Transients

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Transient signal

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Transients

Is there a population of powerful, irregular, transient sources?

What are they?

How do they generate the energy they emit?

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Transients

  • Pulsar is a special case of transient phenomena (periodic)
  • Giant pulses
  • Supernova
  • Bursters
  • ETI

​

requires:

  • fast time constant
  • memory buffer for post analysis
  • wide instantaneous, fully-sampled FoV

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The Unknown

“These are the�wrong questions!”

Woody Allen, Stardust Memories

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Examples of Wrong Questions

If you walk so far that you reach the end of the Earth, will you fall over the edge? Will you fall forever? What supports the Earth?

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Examples of Wrong Questions

How fast are we moving with respect to the ether?

What might have been a better question?

Is there an ether?

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Is there a Big Picture?

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Examples of Wrong Questions

How can I make the General Theory of Relativity compatible with the Steady State Universe?

oops

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Examples of Wrong Questions

What is north of the North Pole?

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Examples of Wrong Questions

What happened before the Big Bang?

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Examples of Wrong Questions

What is the speed of light?

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The Unknown

  • New discoveries always result from observations in new parameter space
    • sensitivity
    • spatial resolution
    • spectral resolution
    • polarisation
    • time domain
    • observing speed (multibeaming)
  • eg. CMB, pulsars, extra solar planets,…

SKA improves all of these

SKA is designed for the Key Projects but with an overriding design philosophy of flexibility to maximise the likelihood of new discoveries

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Discoveries are made…

  • Serendipitously in the course of planned surveys
    • New class of transients
    • New population of faint objects (galaxies, etc)

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And discoveries are made…

  • By using an instrument in a new way
    • Proposals inspired by new questions

SKA for the user…

How much will the Key Projects dominate telescope time?

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Scientific Motivation

?

Tests of gravity

Epoch of Reionisation

Cosmic Magnetism

Cradle of Life

Large Scale Structure

Transient Universe

The Unknown

S.A. Torchinsky (60 of 60)

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Cambridge, 25 August 2008