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 1
Overview of new facilities at radio wavelengths n Many other talks on mm and submm results so I will concentrate on cm and m wavelengths – ie freq < 30 GHz n n n GMRT (3 x VLA at low frequency) LOFAR (very low frequency, multibeaming, multi-user) EVLA (VLA with bandwidth) ATA (16 x 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 2
SKA 3
Unique SKA traits for cosmology n sensitivity 106 m 2. HI out to z=3 – cost of collecting area reduced by consumer electronics n Fo. V - at least 1 deg 2, maybe 100 deg 2 – Moores law n Simultaneous observations at all frequencies – specs call for 0. 1 to 25 GHz – more likely is (0. 1 -0. 7) + (0. 7 -2) + (2 -20) GHz EVLA I – driven by the antenna technology LOFAR first 4
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 Ø and. . . Exploration of the unknown { 5
o 15 Mpc at z = 2 SKA’s 1 field-of-view SKA 20 cm and x 100 possible! SKA 6 cm HST ALMA 6
Why use HI for Surveys? n n Most abundant element in the Universe Simplest constituent of the Universe – We may be able to understand it n Provides the fuel for star formation – Hence necessary to interpret star formation rates n n Simultaneous velocities and line widths Bias’s surveys to late type galaxies – Avoids some of the non-linear effects of clustering 7
The 10 Gyr gap in the Gas Evolution History of the Universe Models imply HI (1+z)2 -3 (+Pei et No data al 1999) DLAs Parkes multibeam HIPASS ASA 2005 L S_S 8
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 m 2) 120 hours (5 days) 0. 1 SKA (100, 000 m 2) 7 minutes Full SKA (1, 000 m 2) 5 seconds Zwaan et al. (2001) A 2218 z=0. 18 WSRT 12 x 18 9 hr
CMB acoustic peaks 10
Simulation of Evolution of Acoustic Oscillations TIME 11
Probing Dark Energy with the SKA n n Standard ruler based on baryonic oscillations (wriggles) Need to reach z ~ 1 – Current limit z = 0. 2 so > x 25 in sensitivity n Optimum strategy is the survey the largest area – Minimise cosmic variance n n n Large Fo. V makes this practical HI selection strong bias to late type galaxies SKA Fo. V=1 sq deg in 1 year $1 B and 2020 – 109 galaxies, 0 < z < 1. 5 Δω =0. 01 n Or 1/10 area SKA phase I with Fo. V=100 sq deg $0. 2 B and 2012 12
Epoch of Re-ionization at radio wavelengths n n Look at effects of the re-ionization on the HI Look at the sources of re-ionization 13
High Redshift HI Experiments n n Bebbington (1985); Uson; et alia Current generation: – – – n PAST 21 CMA (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 14
D. H. O. Bebbington a radio search for primordial pancakes Redshift not known Technology well developed Black~60 m. Jy/beam 5 Aug 2005 Mon. Not. R. astr. Soc. (1986) 218, 577 -585 Don Backer 15
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 16
A Global Eo. R Experiment n Cosmological Re-Ionization Experiment – Co. RE – Ekers, Subramanian, Chippendale - ATNF n n n Measurement of any m. K 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 17
Global Eo. R is challenging n n Cant use spatial structure to remove foregrounds Needs 50, 000: 1 spectral dynamic range over an octave bandwidth – Spectral contaminants (additive) – Bandpass calibration (multiplicative) n Quality is important here: not quantity. – The telescope required is a precision instrument, not a big bucket. Ravi Subramanyan 18
Antenna modeling: n n Need a design with minimum frequency dependence 3 D beam shape of the pyramidal spiral antenna Ravi Subramanyan 19
Co. RE Antenna n 2 -arm log-spiral winding – 4 arm variation is possible n Support structure – Styrofoam pyramid – Foam, glue and paint tested using the Australia Telescope interferometer Ravi Subramanyan 20
Iwo-Jima to Eo. R 21
Interference environment in Australia Sydney : 4 million people Narrabri : 7000 Mileura : 4 80 --- 1600 MHz Ravi Subramanyan 22
PAPER @ Mileura? Walsh Homestead CSIRO RFI van at SKA core site PAPER site to south? 5 Aug 2005 Don Backer 23
21 cm fluctuations Observability Error in noise power PAST LOFAR SKA n Zaldarriaga et al – Ap. J 608, 622 (2004) – 4 w integration Cleaned foreground ! LOFAR SKA 24
The best way to search for HI in the epoch of re-ionization? n n HI redshifted to z=6 (200 MHz) to z=17 (80 MHz) Global signal – Easily detectable but needs spectral dynamic range of >105 : 1 n Statistical detection of fluctuations – PAPER (1 o) – PAST, MWA, LOFAR (3’) – Extreme control of foreground leakage necessary n Direct detection of structure – Needs full SKA MIT Telescope and Mileura Sunset July 2005 Ekers - Bali 25
Some comments on foregrounds n Foreground is 103 - 105 x Eo. R signal – depending on resolution and z n n 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 n Frequency structure in the array sidelobes – Keep antenna sidelobes low – Model and subtract source sidelobes (over whole sky) 26
SKA observation of HI absorption in the Eo. R Cyg A at z =10 S = 20 m. Jy SKA: 10 days, 1 k. Hz Carilli 2002 27
Searching for redshifted CO with the SKA n CO is redshifted into the cm bands – 20 Ghz CO(1 -0) at z=5, CO (2 -1) at z=10 n very complimentary to ALMA Also ACTA and EVLA I – ALMA can only study high transitions at high redshift » (CO 7 -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 n Blind searching becomes possible with SKA – wide Fo. V at cm wavelength (>25 x ALMA) – Relatively wider bandwidth n eg SKA blind survey (Carilli and Blain 2002) – 15 sources/hr with z>4 using redshifted CO (1 -0) at 20 GHz 28
Future Sensitivity HST VLA SKA 29
Radio Source Counts Starburst Radio galaxy/AGN ? SKA VLA B 2 3 C 30
Radiometric Redshifts n M 82 Spectrum Condon Ann Rev. 30: 576 -611 (1992) 1202 -0725 (z = 4. 7) 1335 -0415 (z = 4. 4) n Radiometric redshifts Carilli Ap J 513 (1999) Synchrotron Dust Free-free SKA 2 July 2002 ALMA R. Ekers - Square Km Array n Positions 31
Radio Galaxy - 4 C 41. 17 redshift 3. 8 n Alignment of radio jets (contours) with other tracers of star formation – VLA radio image × HST F 702 × HST F 569 × Ly-α van Breugel (1985) 13 July 05 R D Ekers 32
BR 1202 -0725 Redshift 4. 69 Radio VLA Carilli et. al. 2002 n CO(2 -1) HST K-band Carilli et. al. 2002 Hu et. al. 1996 Ap. J Radio – CO – Ly alpha – Optical are all aligned ! Klamer, Ekers, et al, Ap. J 612, L 97 13 July 05 R D Ekers 33
CMB – special purpose instruments DASI with sun dogs 35
CMB foregrounds – role for ground based telescopes? n n Acknowledged as the main problem for future experiments (Bouchet, Lawrence) Measure structures to better understand the physics – Eg spinning dust, galactic polarization n Look after the point source foregrounds – Here we can take advantage of higher angular resolution to separate out and measure the point source foreground – AT 20 G all sky survey at 20 GHz with ATCA » » 1/3 southern sky completed to 50 -100 m. Jy Less variability than expected No power law spectra! No new class of objects 36
S-Z n Clusters – Excellent for S-Z because non-thermal confusion can be subtracted – 10<ν<20 GHz – Optimum sensitivity – Optimum resolution n Protospheroids – Few μK (very hard with current telescopes) – Only SKA has adequate sensitivity 37
Magnetism and Radio Astronomy Most of what we know about cosmic magnetism is from radio waves! n Faraday rotation → B|| n Synchrotron emission → orientation, |B | n Zeeman splitting → B|| Stokes I Kazès et al (1991) Fletcher & Beck (2004) Stokes V 2005 38
The Origin and Evolution of Cosmic Magnetism: n 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. n Is there a connection between the formation of magnetic fields and the formation of structure in the early Universe? n When and how are the first magnetic fields in the Universe generated? 39
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) 40
Exploring the unknown The universe is not only queerer than we suppose, but queerer than we CAN suppose. J. B. S. Haldane 41
Exploring the unknown n 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 n but the SKA greatly enlarges the volume of parameter space explored – sensitivity and Fo. V 106 x VLA – New classes of rare objects – Access to the high redshift universe 42
Key Discoveries in Radio Astronomy# Discovery Date Cosmic radio emission Non-thermal cosmic radiation Solar radio bursts Extragalactic radio sources 21 cm 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 s 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 n The number of discoveries made with special purpose instruments has declined 45
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 46
A possible SKA Pathfinder n n n One possibility 1000 x 15 m dishes 0. 6 – 2 GHz Wide field-of-view (35 deg 2) – 10 x 10 Focal Plane Array – 10% SKA area Construction 2009 -2012 International collaboration a fundamental component 47
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 48
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