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21cm cosmology

21cm cosmology. T. Chang, UP, J. Peterson, P. McDonald PRL 100, 091303 (2008) UP, L. Staveley-Smith, J. Peterson, T. Chang, MNRAS, 394, 6 (2009). 21cm: HI hyperfine transition. Hydrogen is the most abundant element in the universe

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21cm cosmology

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  1. 21cm cosmology T. Chang, UP, J. Peterson, P. McDonald PRL 100, 091303 (2008) UP, L. Staveley-Smith, J. Peterson, T. Chang, MNRAS, 394, 6 (2009)

  2. 21cm: HI hyperfine transition • Hydrogen is the most abundant element in the universe • Hyperfine transition when electron and proton spins flip: change in magnetic moment • h ν =α4 me c2 (me/mp) • ν=1420.40575 MHz

  3. Image courtesy of NRAO/AUI and Chung et al., Columbia University

  4. The 21 cm universe • Cosmological LSS treasure grove (UP04, Loeb&Zaldarriaga 04, Lewis&Challinor 07, etc) • Up to 1018 modes: z=50 (Jeans/Hubble)3 • Physics: Lensing, gravity waves, primordial NG, BAO, AP • GW to r ~ 10-8 • fNL~ 10-4 • Astrophysics: EoR, galaxy evolution • Experiments NOW EoR: GMRT/LOFAR MWA CHIME/GBT SDSS Tegmark & Zaldarriaga 08

  5. Hydrogen: Then and Now • 21cm first detected 1952 (Ewen and Purcell) • Previous most distant emission redshift: z=0.3 using 1960’s telescope (WSRT) • Epoch of Reionization: z ~ 9 • z=1-3 BAO: dark energy from geometric distance measurement

  6. Cosmic Reionization log10 T (mK) (Iliev, Mellema, Pen, Shapiro 2006) Largest radiative transfer cosmological reionization simulations: 1 degree FOV. Detection in 21cm hyperfine transition with radio telescopes. Structure on large scales (>20’). See also Furlanetto, Oh, Zaldarriaga, Zahn, Morales, Mesinger, Croft, Ciardi, etc

  7. Iliev et al 2008

  8. Foreground: Galactic Synchrotron Haslam 408 MHz Much brighter than signal, but no spectral structure

  9. Indian Giant Meterwave Radio Telescope 30 dishes @45m ea. Operates in 2m band Collaborators: Y. Gupta (chief scientist), Rajaram Nityananda (director), J. Roy, J. Peterson (CMU), C. Hirata (IAS), T. Chang (CITA), J. Odegova (Toronto), K. Sigurdson (UBC)

  10. Radio Frequency Interference

  11. Intensity Mapping • Stars get fainter with distance: hard to see individually at cosmological distance. Galaxies still visible. • Galaxies get fainter with distance: hard to see in HI. Large scale structure still visible? • Large scale structure is LARGE: degree scale. High resolution not needed. • Modest size, monolithic radio telescopes needed. (CPPM 2008, Wyithe&Loeb 2008)

  12. From: talk by O. Lahav

  13. Baryon Acoustic Oscillations – Dark Energy Probe • CMB acoustic oscillations: imprinted standard ruler, 100 Mpc. • Present in current matter distribution • Kinematic metric of universe WMAP5 and other, Nolta et al (2008)

  14. Present LSS BAO Detections Percival et al 2007 • Percival et al 2007 Eisenstein et al 2005

  15. Komatsu et al, 2008

  16. Radio Mapping Experiments Redshifted 21cm Hydrogen transition: 300MHz-1.4 GHz, radio maps Large area survey, large field of view, low surface brightness: like CMB. Signal ~ 50-200 µK Foregrounds large -- ~K, but smooth (spatially and spectrally). Potential challenges: frequency dependent beam, polarization leakage, calibration Pilot data from Parkes, GBT (UP et al, 3/2009)

  17. Chang et al 2009 (submitted)

  18. Keck-DEEP2 GBT z=0.9 cross correlation

  19. Dedicated Survey Experiment • Low frequency technology cheap, modest size: (100 m)2 to z<2 • Large field of view: receiver arrays • High surface brightness sensitivity: compact arrays • Stable, reliable: no moving parts • Technologies: aperture arrays (Wyithe, Loeb, Geil 2008), cylinders (Peterson et al)

  20. Darwin AUSTRALIA Brisbane Sydney Perth + Molonglo Adelaide Canberra Melbourne Hobart Northern Cross Molonglo Ooty Cambridge Pushchino

  21. CMU cylinder under construction: U. Seljak, J. Peterson, K. Bandura, K. Sigurdson

  22. CHIME Cosmic (Canadian) Hydrogen Imaging Experiment Proposal to CFI for cylinders in Penticton (DRAO, BC) (see also CRT: DAPNA/FNAL/IAA) Collaboration: M. Halpern, K. Sigurdson (UBC), M. Dobbs (McGill), UP, J.R. Bond, T. Chang (CITA), J. Peterson (CMU) + others

  23. DRAO Penticton CLAR Site

  24. Mapping LSS

  25. BAO survey volumes

  26. Cosmic Variance Limited Hubble Surveys Chang, UP, Peterson, McDonald, PRL 100, 091303, March 5, 2008

  27. Conclusions • 21cm cosmology: cosmic treasure trove? • Lack of substantial telescope investment in 30 years. • Working towards detection at z=8.6 • Intensity Mapping: 21cm unresolved galaxies, accessible in redshift desert z=1-3. • Initial HI detection with GBT at z~1 • Baryon Acoustic Oscillations – geometric measure of the universe and dark energy • Prototypes and observations under way. Cylinder telescopes a promising technology.

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