1

Future radio observations of the Future radio observations of the high redshift universehigh redshift universe

Open Questions in CosmologyMunich Aug 22-26 2005

Ron EkersCSIRO

2

Overview of new facilities at Overview of new facilities at radio wavelengthsradio wavelengths

Many other talks on mm and submm results so I will concentrate on cm and m wavelengths– ie freq < 30GHz

GMRT (3x VLA at low frequency) LOFAR (very low frequency, multibeaming, multi-user) EVLA (VLA with bandwidth) ATA (16x VLA field of view, multi-user) SKA – all of above and some Continued role for special purpose experiments

– Mainly at very high and very low frequencies

3

SKASKA

4

Unique SKA traits for Unique SKA traits for cosmologycosmology

sensitivity 106 m2. HI out to z=3– cost of collecting area reduced by consumer electronics

FoV - at least 1 deg2, maybe 100 deg2

– Moores law

Simultaneous observations at all frequencies– specs call for 0.1 to 25GHz

– more likely is (0.1-0.7) + (0.7-2) + (2-20) GHz

– driven by the antenna technology EVLA I first

LOFAR

5

SKA Key Science Goals SKA Key Science Goals

1) Probing the dark ages before the first

stars

2) Evolution of galaxies and large scale

structure in the universe

3) Origin and evolution of cosmic

magnetism

4) The cradle of life (terrestrial planets)

5) Strong field tests of gravity via pulsars

and black holes

and... Exploration of the unknown{

6

SKA’s 1SKA’s 1oo field-of-view field-of-view

HST SKA 6cm

ALMA

15 M

pc

at

z =

2

SKA 20 cmand x100 possible!

7

Why use HI for Surveys?Why use HI for Surveys?

Most abundant element in the Universe Simplest constituent of the Universe

– We may be able to understand it

Provides the fuel for star formation– Hence necessary to interpret star formation rates

Simultaneous velocities and line widths Bias’s surveys to late type galaxies

– Avoids some of the non-linear effects of clustering

The 10 Gyr gap in the Gas The 10 Gyr gap in the Gas Evolution History of the UniverseEvolution History of the Universe

HIPASS

DLAs

No dataModels imply HI (1+z)2-3 (+Pei et al 1999)

Parkes multibeam

9

Why collecting area Why collecting area is critical for HI...is critical for HI...

Approximate time needed to detect an M* spiral galaxy (MHI = 6 x 109 Msun) at z=0.1:

Parkes (3200 m2) 120 hours (5 days)

0.1 SKA (100,000 m2) 7 minutes

Full SKA (1,000,000 m2) 5 seconds

Sensitivity: SNR A.t

for a radio telescope (background-noise limited) with collecting area A, integration time t.

For any given collecting area, there is an effective zmax beyond which HI emission is effectively undetectable.

Zwaan et al. (2001)

A2218 z=0.18

WSRT 12x18 hr

10

CMB acoustic peaksCMB acoustic peaks

11

Simulation of Simulation of Evolution of Acoustic OscillationsEvolution of Acoustic Oscillations

TIM

E

12

Probing Dark EnergyProbing Dark Energy with the SKA with the SKA

Standard ruler based on baryonic oscillations (wriggles) Need to reach z ~ 1

– Current limit z = 0.2 so > x25 in sensitivity

Optimum strategy is the survey the largest area– Minimise cosmic variance

Large FoV makes this practical HI selection strong bias to late type galaxies SKA FoV=1sq deg in 1 year

– 109 galaxies, 0 < z < 1.5 Δω =0.01

Or 1/10 area SKA phase I with FoV=100sq deg

$1B and 2020

$0.2B and 2012

13

Epoch of Re-ionizationEpoch of Re-ionization at radio wavelengths at radio wavelengths

Look at effects of the re-ionization on the HI Look at the sources of re-ionization

5 Aug 2005 Don Backer 14

High Redshift HI ExperimentsHigh Redshift HI Experiments

Bebbington (1985); Uson; et alia Current generation:

– PAST 21CMA (Pen, Peterson, Wang: China)– LOFAR (de Bruyn et alia: The Netherlands)– MWA (Lonsdale, Hewitt et alia: WA)– PAPER (Backer, Bradley: NRAO GBWA?)– CORE (Ekers, Subramanian, Chippendale: WA)

Next generation:– SKA (International)

$

$$$$$

$$$$$

$$

$$

5 Aug 2005 Don Backer 15

Black~60 mJy/beam

D.H.O. BebbingtonD.H.O. Bebbingtona radio search for primordial pancakesa radio search for primordial pancakes

Mon. Not. R. astr. Soc. (1986) 218, 577-585

Redshift not known

Technology well developed

5 Aug 2005 Don Backer 16

Shaver et al. Shaver et al.

“Can the reionization epoch be detected as a global signature in the cosmic background?”

P.A. Shaver, R.A. Windhorst, P. Madau, and A.G. de Bruyn

Astron. Astrophys. 345, 380–390 (1999)

Ravi Subramanyan 17

A Global EoR ExperimentA Global EoR Experiment

Cosmological Re-Ionization Experiment – CoRE– Ekers, Subramanian, Chippendale - ATNF

Measurement of any mK spectral features in the global low-frequency radio background

Antenna with one steradian beam 110-230 MHz band : corresponding to z = 5-12

Ravi Subramanyan 18

Global EoR is challengingGlobal EoR is challenging

Cant use spatial structure to remove foregrounds Needs 50,000:1 spectral dynamic range over an

octave bandwidth– Spectral contaminants (additive) – Bandpass calibration (multiplicative)

Quality is important here: not quantity. – The telescope required is a precision instrument, not a

big bucket.

Ravi Subramanyan 19

Antenna modeling:Antenna modeling:

Need a design with minimum frequency dependence

3D beam shape of the pyramidal spiral antenna

Ravi Subramanyan 20

CoRE AntennaCoRE Antenna

2-arm log-spiral winding – 4 arm variation is possible

Support structure– Styrofoam pyramid

– Foam, glue and paint tested using the Australia Telescope interferometer

21

Iwo-Jima to EoRIwo-Jima to EoR

Ravi Subramanyan 22

Interference environment Interference environment in Australiain Australia

80 --- 1600 MHz

Sydney : 4 million people

Narrabri : 7000

Mileura : 4

5 Aug 2005 Don Backer 23

PAPER PAPER @ Mileura?@ Mileura?

CSIRO RFI van at SKA core site

PAPER site to south?

Walsh Homestead

24

21cm fluctuations21cm fluctuationsObservabilityObservability

Zaldarriaga et al – ApJ 608, 622 (2004)

– 4w integration

LOFAR

SKA

LOFAR SKAPAST

nois

e po

wer

Err

or in

nois

e po

wer

Cleaned foreground !

July 2005 Ekers - Bali 25

The best way to search for HI The best way to search for HI in the epoch of re-ionization?in the epoch of re-ionization?

HI redshifted to z=6 (200MHz) to z=17 (80MHz) Global signal

– Easily detectable but needs spectral dynamic range of >105 : 1

Statistical detection of fluctuations– PAPER (1o)

– PAST, MWA, LOFAR (3’)

– Extreme control of foreground

leakage necessary

Direct detection of structure– Needs full SKA

MIT Telescope and Mileura Sunset

26

Some comments on Some comments on foregroundsforegrounds

Foreground is 103 - 105 x EoR signal– depending on resolution and z

Continuum - both discrete and diffuse Some line Search in frequency removes most of the problem Frequency structure due to Faraday Rotation in the

polarized galactic synchrotron emission– Need full polarization, and polarization purity

Frequency structure in the array sidelobes– Keep antenna sidelobes low – Model and subtract source sidelobes (over whole sky)

Very different to CMB

Very different to CMB

27

SKA observation of HI SKA observation of HI absorption in the EoRabsorption in the EoR

Cyg A at z =10S = 20mJy

SKA: 10days, 1kHz

Carilli 2002

28

Searching for redshifted Searching for redshifted CO with the SKACO with the SKA

CO is redshifted into the cm bands– 20Ghz CO(1-0) at z=5, CO (2-1) at z=10

very complimentary to ALMA– ALMA can only study high transitions at high redshift

» (CO7-6 at z=8)– low excitation transitions are more likely at high z– easier to compare with observations in the local universe– SKA sensitivity more than compensates for transition strength

Blind searching becomes possible with SKA– wide FoV at cm wavelength (>25x ALMA)– Relatively wider bandwidth

eg SKA blind survey (Carilli and Blain 2002)– 15 sources/hr with z>4 using redshifted CO (1-0) at 20GHz

Also ACTA and EVLA I

29

VLA

Future SensitivityFuture Sensitivity

HST SKA

Radio Source CountsRadio Source Counts

3CVLA B2SKA

Radio galaxy/AGN

Starburst

?

2 July 2002 R. Ekers - Square Km Array 31

Radiometric RedshiftsRadiometric Redshifts

M82 Spectrum Condon Ann Rev. 30: 576-611 (1992)

Radiometric redshifts Carilli Ap J 513 (1999)

Positions

Synchrotron

Free-free

Dust

1202-0725 (z = 4.7)1335-0415 (z = 4.4)1335-0415 (z = 4.4)

SKA ALMA

13 July 05 R D Ekers 32

Radio Galaxy - 4C41.17Radio Galaxy - 4C41.17redshift 3.8redshift 3.8

Alignment of radio jets (contours) with other tracers of star formation– VLA radio image

HST F702

HST F569

Ly-α van Breugel (1985)

13 July 05 R D Ekers 33

BR 1202-0725 BR 1202-0725 Redshift 4.69Redshift 4.69

CO(2-1)

Carilli et. al. 2002Carilli et. al. 2002

Radio VLA

Hu et. al. 1996 ApJ

HST K-band

Radio – CO – Ly alpha – Optical are all aligned !Klamer, Ekers, et al, ApJ 612, L97

35

CMB – special purpose CMB – special purpose instruments instruments

DASI with sun dogs

36

CMB foregrounds – role for CMB foregrounds – role for ground based telescopes?ground based telescopes?

Acknowledged as the main problem for future experiments (Bouchet, Lawrence)

Measure structures to better understand the physics– Eg spinning dust, galactic polarization

Look after the point source foregrounds– Here we can take advantage of higher angular resolution to

separate out and measure the point source foreground

– AT20G all sky survey at 20GHz with ATCA» 1/3 southern sky completed to 50-100mJy

» Less variability than expected

» No power law spectra!

» No new class of objects

37

S-ZS-Z

Clusters– Excellent for S-Z because non-thermal confusion can

be subtracted

– 10<ν<20GHz

– Optimum sensitivity

– Optimum resolution

Protospheroids– Few μK (very hard with current telescopes)

– Only SKA has adequate sensitivity

2005 38

Magnetism Magnetism and Radio and Radio

AstronomyAstronomyMost of what we know about cosmic magnetism is from radio waves! Faraday rotation → B|| Synchrotron emission → orientation, |B|

Zeeman splitting → B||

Stokes I

Stokes V

Kazès et al (1991)

Fletcher & Beck (2004)

39

The Origin and Evolution of The Origin and Evolution of Cosmic Magnetism: Cosmic Magnetism:

all-sky radio continuum survey with SKA– measure rotation measures for 108 polarized extragalactic sources,

with an average spacing between sightlines of ~60”.

– This will completely characterize the evolution of magnetic fields in galaxies and clusters from redshifts z > 3 to the present.

Is there a connection between the formation of magnetic fields and the formation of structure in the early Universe?

When and how are the first magnetic fields in the Universe generated?

2004 Kramer - Leiden retreat (updated) 40

Pulsars as Pulsars as Gravitational Wave DetectorsGravitational Wave Detectors

• Millisecond pulsars act as arms of huge detector:

Pulsar Timing Array:Pulsar Timing Array:Look for global spatial Look for global spatial

pattern in timing residualspattern in timing residuals!!

Pulsar Timing Array:Pulsar Timing Array:Look for global spatial Look for global spatial

pattern in timing residualspattern in timing residuals!!

LISAPulsars AdvancedLIGO

• Complementary in Frequency!

SKA

QSO astrometry QSO astrometry too!too!

41

Exploring the unknownExploring the unknown

The universe is not only queerer than we suppose,

but queerer than we CAN suppose.

J.B.S.Haldane

42

Exploring the unknownExploring the unknown

Astronomy is not an experimental science Experiments which open new parameter space are most likely

to make transformational discoveries cm radio astronomy has opened all the available parameter

space– space, time, frequency, polarization

but the SKA greatly enlarges the volume of parameter space explored– sensitivity and FoV 106 x VLA

– New classes of rare objects

– Access to the high redshift universe

Key Discoveries Key Discoveries in Radio Astronomy#in Radio Astronomy#

Discovery DateCosmic radio emission 1933

Non-thermal cosmic radiation 1940

Solar radio bursts 1942

Extragalactic radio sources 1949

21cm line of atomic hydrogen 1951

Mercury & Venus spin rates 1962, 5

Quasars 1962

Cosmic Microwave Background

1963

Confirmation of General Relativity (time delay + light bending)

1964, 70

Discovery DateCosmic masers 1965

Pulsars 1967

Superluminal motions in AGN 1970

Interstellar molecules and GMCs 1970s

Binary neutron star / gravitational radiation

1974

Gravitational lenses 1979

First extra-solar planetary system 1991

Size of GRB Fireball 1997

# This is a short list covering only metre and centimetre wavelengths.

Wilkinson, Kellermann, Ekers, Cordes & Lazio (2004)

45

Key Discoveries :Key Discoveries :Type of instrumentType of instrument

The number of discoveries made with special purpose instruments has declined

Key Discoveries in Radio Astronomy

0

1

2

3

4

5

6

7

1930 1940 1950 1960 1970 1980 1990

Date

Nu

mb

er/

de

ca

de

Specialized

General-purpose

46

Proposed SKA TimelineProposed SKA Timeline

2006 2009 2013 202020112007 2008

Site bid

Site ranking

Technology selection Full SKA operational

SKA production readiness review

Demonstrator developments

SKA Pathfinder construction

SKA Construction 2070+

47

One possibility 1000 x 15m dishes 0.6 – 2 GHz Wide field-of-view (35deg2)

– 10 x 10 Focal Plane Array– 10% SKA area

Construction 2009-2012 International collaboration a

fundamental component

A possible SKA PathfinderA possible SKA Pathfinder

48

SKA science book: SKA science book:

available onlineavailable online

Science with the Square Kilometre Array,

eds: C. Carilli, S. Rawlings,

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

www.skatelescope.org