Transcript Future radio observations of the high redshift universe

Future radio observations of the
high redshift universe
Open Questions in Cosmology
Munich Aug 22-26 2005
Ron Ekers
CSIRO
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Overview of new facilities at
radio wavelengths
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Many other talks on mm and submm results so I will
concentrate on cm and m wavelengths
– ie freq < 30GHz
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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
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SKA
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Unique SKA traits for
cosmology
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sensitivity  106 m2. HI out to z=3
– cost of collecting area reduced by consumer electronics
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FoV - at least 1 deg2, maybe 100 deg2
– Moores law
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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
EVLA I
– driven by the antenna technology
LOFAR
first
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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
{
5
o
15 Mpc at z = 2
SKA’s 1 field-of-view
SKA 20 cm
and x100
possible!
SKA 6cm
HST
ALMA
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Why use HI for Surveys?
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Most abundant element in the Universe
Simplest constituent of the Universe
– We may be able to understand it
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Provides the fuel for star formation
– Hence necessary to interpret star formation rates
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Simultaneous velocities and line widths
Bias’s surveys to late type galaxies
– Avoids some of the non-linear effects of clustering
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The 10 Gyr gap in the Gas
Evolution History of the Universe
Models imply
HI (1+z)2-3
No data
(+Pei et al 1999)
DLAs
Parkes
multibeam
HIPASS
Why collecting area
is critical for HI...
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.
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
Zwaan et al. (2001)
A2218 z=0.18
WSRT 12x18
9 hr
CMB acoustic peaks
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Simulation of
Evolution of Acoustic Oscillations
TIME
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Probing Dark Energy
with the SKA
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Standard ruler based on baryonic oscillations (wriggles)
Need to reach z ~ 1
– Current limit z = 0.2 so > x25 in sensitivity
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Optimum strategy is the survey the largest area
– Minimise cosmic variance
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Large FoV makes this practical 
HI selection  strong bias to late type galaxies
SKA FoV=1sq deg in 1 year
$1B and 2020
– 109 galaxies, 0 < z < 1.5 Δω =0.01
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Or 1/10 area SKA phase I with FoV=100sq deg
$0.2B and 2012
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Epoch of Re-ionization
at radio wavelengths
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Look at effects of the re-ionization on the HI
Look at the sources of re-ionization
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High Redshift HI Experiments
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Bebbington (1985); Uson; et alia
Current generation:
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–
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PAST 21CMA (Pen, Peterson, Wang: China) $$
LOFAR (de Bruyn et alia: The Netherlands) $$$
MWA (Lonsdale, Hewitt et alia: WA) $$
PAPER (Backer, Bradley: NRAO GBWA?) $$
CORE (Ekers, Subramanian, Chippendale: WA) $
Next generation:
– SKA (International) $$$$$
5 Aug 2005
Don Backer
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D.H.O. Bebbington
a radio search for primordial pancakes
Redshift
not known
Technology
well developed
Black~60 mJy/beam
5 Aug 2005
Mon. Not. R. astr. Soc.
(1986) 218, 577-585
Don Backer
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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)
5 Aug 2005
Don Backer
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A Global EoR Experiment
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Cosmological Re-Ionization Experiment – CoRE
– Ekers, Subramanian, Chippendale - ATNF
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Measurement of any mK spectral features in the
global low-frequency radio background
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Antenna with one steradian beam
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110-230 MHz band : corresponding to z = 5-12
Ravi Subramanyan
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Global EoR is challenging
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Cant use spatial structure to remove foregrounds
Needs 50,000:1 spectral dynamic range over an
octave bandwidth
– Spectral contaminants (additive)
– Bandpass calibration (multiplicative)
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Quality is important here: not quantity.
– The telescope required is a precision instrument, not a
big bucket.
Ravi Subramanyan
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Antenna modeling:
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Need a design with
minimum frequency
dependence
3D beam shape of the
pyramidal spiral
antenna
Ravi Subramanyan
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CoRE Antenna
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2-arm log-spiral winding
– 4 arm variation is possible
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Support structure
– Styrofoam pyramid
– Foam, glue and paint
tested using the Australia
Telescope interferometer
Ravi Subramanyan
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Iwo-Jima to EoR
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Interference environment
in Australia
Sydney : 4 million people
Narrabri : 7000
Mileura : 4
80 --- 1600 MHz
Ravi Subramanyan
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PAPER
@ Mileura?
Walsh Homestead
CSIRO RFI van at SKA core site
PAPER site to south?
5 Aug 2005
Don Backer
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21cm fluctuations
Observability
Error in
noise power
noise power
PAST
LOFAR
SKA
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Zaldarriaga et al
– ApJ 608, 622 (2004)
– 4w integration
Cleaned foreground !
LOFAR
SKA
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The best way to search for HI
in the epoch of re-ionization?
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HI redshifted to z=6 (200MHz) to z=17 (80MHz)
Global signal
– Easily detectable but needs spectral dynamic range of >105 : 1
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Statistical detection of fluctuations
– PAPER (1o)
– PAST, MWA, LOFAR (3’)
– Extreme control of foreground
leakage necessary
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Direct detection of structure
– Needs full SKA
MIT Telescope and Mileura Sunset
July 2005
Ekers - Bali
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Some comments on
foregrounds
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Foreground is 103 - 105 x EoR signal
– depending on resolution and z
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Very different
to CMB
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
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Frequency structure in the array sidelobes
– Keep antenna sidelobes low
– Model and subtract source sidelobes (over whole sky)
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SKA observation of HI
absorption in the EoR
Cyg A at z =10
S = 20mJy
SKA: 10days, 1kHz
Carilli 2002
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Searching for redshifted
CO with the SKA
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CO is redshifted into the cm bands
– 20Ghz  CO(1-0) at z=5, CO (2-1) at z=10
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very complimentary to ALMA
Also ACTA
and EVLA I
– 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
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Blind searching becomes possible with SKA
– wide FoV at cm wavelength (>25x ALMA)
– Relatively wider bandwidth
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eg SKA blind survey (Carilli and Blain 2002)
– 15 sources/hr with z>4 using redshifted CO (1-0) at 20GHz
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Future Sensitivity
HST
VLA
SKA
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Radio Source Counts
Starburst
Radio galaxy/AGN
?
SKA
VLA
B2
3C
Radiometric Redshifts
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M82 Spectrum
Condon Ann Rev.
30: 576-611 (1992)
1202-0725 (z = 4.7)
1335-0415
1335-0415
(z = 4.4)
(z = 4.4)
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Radiometric
redshifts
Carilli
Ap J 513 (1999)
Synchrotron
Dust
Free-free
SKA
2 July 2002
ALMA
R. Ekers - Square Km Array
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Positions
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Radio Galaxy - 4C41.17
redshift 3.8
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Alignment of radio jets (contours)
with other tracers of star formation
– VLA radio image
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HST F702
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HST F569
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Ly-α
van Breugel (1985)
13 July 05
R D Ekers
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BR 1202-0725
Redshift 4.69
Radio VLA
Carilli et. al. 2002
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CO(2-1)
HST K-band
Carilli et. al. 2002
Hu et. al. 1996 ApJ
Radio – CO – Ly alpha – Optical are all aligned !
Klamer, Ekers, et al, ApJ 612, L97
13 July 05
R D Ekers
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CMB – special purpose
instruments
DASI with sun dogs
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CMB foregrounds – role for
ground based telescopes?
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Acknowledged as the main problem for future experiments
(Bouchet, Lawrence)
Measure structures to better understand the physics
– Eg spinning dust, galactic polarization
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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
»
»
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1/3 southern sky completed to 50-100mJy
Less variability than expected
No power law spectra!
No new class of objects
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S-Z
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Clusters
– Excellent for S-Z because non-thermal confusion can
be subtracted
– 10<ν<20GHz
– Optimum sensitivity
– Optimum resolution
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Protospheroids
– Few μK (very hard with current telescopes)
– Only SKA has adequate sensitivity
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Magnetism
and Radio Astronomy
Most of what we know about cosmic magnetism is from radio waves!
 Faraday rotation → B||
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Synchrotron emission → orientation, |B|
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Zeeman splitting → B||
Stokes I
Kazès et al (1991)
Fletcher & Beck (2004)
Stokes V
2005
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The Origin and Evolution of
Cosmic Magnetism:
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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.
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Is there a connection between the formation of magnetic
fields and the formation of structure in the early Universe?
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When and how are the first magnetic fields in the Universe
generated?
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Pulsars as
Gravitational Wave Detectors
• Millisecond pulsars act as arms of huge detector:
Pulsars LISA Advanced
LIGO
SKA
Pulsar Timing Array:
Look for global spatial
pattern in timing residuals!
2004
QSO astrometry
too!
• Complementary in Frequency!
Kramer - Leiden retreat (updated)
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Exploring the unknown
The universe is not only queerer
than we suppose,
but queerer than we CAN suppose.
J.B.S.Haldane
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Exploring the unknown
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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
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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
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Key Discoveries
in Radio Astronomy#
Discovery
Date
Discovery
Date
Cosmic radio emission
Non-thermal cosmic radiation
Solar radio bursts
Extragalactic radio sources
21cm line of atomic hydrogen
Mercury & Venus spin rates
Quasars
Cosmic Microwave Background
Confirmation of General
Relativity
(time delay + light bending)
1933
1940
1942
1949
1951
1962, 5
1962
1963
1964, 70
Cosmic masers
Pulsars
Superluminal motions in AGN
Interstellar molecules and GMCs
Binary neutron star /
gravitational radiation
Gravitational lenses
First extra-solar planetary system
Size of GRB Fireball
1965
1967
1970
1970s
1974
# This is a short list covering only metre and centimetre wavelengths.
Wilkinson, Kellermann, Ekers, Cordes & Lazio (2004)
1979
1991
1997
Key Discoveries :
Type of instrument
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The number of discoveries made with
special purpose instruments has declined
Key Discoveries in Radio Astronomy
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Specialized
Number/decade
6
General-purpose
5
4
3
2
1
0
1930
1940
1950
1960
Date
1970
1980
1990
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Proposed SKA Timeline
2006 2007 2008 2009
Demonstrator
developments
Site bid
2011
SKA Pathfinder
construction
Technology selection
Site ranking
2020
2013
SKA Construction
2070+
Full SKA operational
SKA production
readiness review
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A possible SKA Pathfinder
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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
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SKA science book:
available online
Science with the Square
Kilometre Array,
eds: C. Carilli, S. Rawlings,
New Astronomy Reviews,
Vol.48, Elsevier, Dec. 2004
www.skatelescope.org
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