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Hydrogen 21cm Cosmology

Hydrogen 21cm Cosmology. Tzu-Ching Chang (ASIAA) Ue-Li Pen, Kiyo Masui (CITA) Jeff Peterson, Kevin Bandura, Tabitha Voytek, Aravind Natarajan (CMU) Pat McDonald (LBNL) Victor Liao (ASIAA). The initial condition.

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Hydrogen 21cm Cosmology

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  1. Hydrogen 21cm Cosmology Tzu-Ching Chang (ASIAA) Ue-Li Pen, Kiyo Masui (CITA) Jeff Peterson, Kevin Bandura, Tabitha Voytek, Aravind Natarajan (CMU) Pat McDonald (LBNL) Victor Liao (ASIAA)

  2. The initial condition • Cosmic Microwave Background fluctuations of 10-5 at z~1100 (surface of last-scattering) WMAP

  3. HEDEX

  4. Dark Energy • Dominates the current energy budget of the Universe • Causes accelerated expansion • Modifies growth of structure • Unknown origins • Most prosaic “explanation” is a cosmological constant • Well established observationally (e.g. SNe) • A sensitive probe - Baryon Acoustic Oscillation

  5. Baryon Acoustic Oscillations • Sound waves in the photon-baryon plasma in the early universe propagate from density perturbations; they freeze out when universe transited from radiation to matter domination (recombination). • Thus they have a characteristic scale of 100 h-1Mpc (~150 Mpc), corresponding to the sound horizon at recombination at z~1100. Courtesy of D. Eisenstein

  6. Baryon Acoustic Oscillation • A more subtle feature when superposed on a complex density field

  7. The oscillation peaks and troughs on the CMB power spectrum are obvious

  8. More subtle on the galaxy distribution at late times (z~0.35) • Sloan Digital Sky Survey

  9. It causes a slight peak in the galaxy correlation function (z~0.35) Eisenstein+ 05

  10. The oscillation peaks and troughs on the large-scale matter power spectrum Reid+ 10

  11. Why is Baryon Acoustic Oscillation (BAO) interesting? • It is a direct demonstration of the gravitational instability paradigm: a feature we see in the CMB 380,000 years after the Big Bang is also seen in an evolved state in the present-day Universe, 13.6 Gyrs after. • The scale of the feature is fixed: it is determined by the scale of the sound horizon at recombination, therefore by the physics in the early Universe. It is a “standard ruler”, and thus is a direct constraint on the geometry of the Universe. • We probe dark energy via its evolution on the expansion rate of the Universe. BAO and CMB, both standard rules, provide an excellent measurement of dark energy properties.

  12. BAO - great tool for precision cosmology Komatsu+ 08

  13. BAO Measurements • BAO feature is present in the distribution of large-scale structure • Can be quantified by imprints on the large-scale matter power spectrum • Galaxies are tracers of large-scale structure; traditionally, we need to measure the 3D position of millions of galaxies in a redshift survey (e.g. SDSS) • Here we propose an alternative: 21-cm

  14. 21cm Line Picture from C. Hirata • Ground-state spin-flip hyperfine transition of neutral hydrogen • Hydrogen: most abundant element, optically thin • Line transition: Probe 3D structure of the Universe • Can be seen in absorption or emission against • the CMB, depending on the spin temperature: • Ts > Tcmb: emission (z < 10) • Ts < Tcmb: absorption ( ~15? < z <~ 150) • Brightness Temperature: 300

  15. The 21cm universe • HI 21cm radiation observable up to z~150 • Up to 1016 modes to z~50(Hubble/Jeans)3 • Physics: Lensing, gravity waves, primordial NG, BAO, AP (Pen 04, Loeb & Zaldarriaga 04, Lewis & Challinor 07, etc.) • Astrophysics: EoR, galaxy formation & evolution • Experiment Now • EoR: GMRT, LOFAR, MWA, PAPER, 21CMA • BAO: GBT, CRT, CHIME EOR LSS SDSS Tegmark & Zaldarriaga 08

  16. 10 21cm Large-Scale Structure 1 Z • Large-scale HI temperature fluctuation; CMB-like, in 3D • Observed frequency: f = 1420/(1+z) MHz • 0.5<z<2.5, HI traces under-lying matter distribution, can be used to measure Baryon Acoustic Oscillations (100 Mpc scale) => dark energy • 6<z<10, Epoch of Reionization, ~20-50 Mpc scale, HI shows tomographic history of reionization => astrophysics M. White LSS; BAO EOR

  17. 21cm emission on galaxy scales • Due to small emissivity, HI in emission is difficult to detect. • Previously, HI direct detection at z~0.2 (Verheijen et al 2007), stacking at z~0.3 (Lah et al. 2007); both on galaxy scales.

  18. 21cm Intensity Mapping • “Intensity Mapping”(Chang et al 2008, Wyithe & Loeb 2008): instead of HI associated with galaxies, interested in HI associated with large-scale structure => measure the collective HI emission from a large region, more massive and luminous, without spatially resolving down to galaxy scales. • Measurement of spatially diffused spectral line, in the confusion-limited regime • Brightness temperature fluctuations on the sky: just like CMB temperature field, but in 3D • Low angular resolution redshift survey: economical

  19. RFI, Galactic Synchrotron foregrounds > 103 signal • HI content, distribution at high-z uncertain 21cm Observational Challenges: Haslam Map at 408 MHz

  20. Green Bank Telescope

  21. Observing HI Large-scale Structure at GBT • Green Bank Telescope: 100 meter in diameter; largest steerable single dish • Observed at 670-910 MHz (0.53<z<1.1) at two of the DEEP2 fields 2 x (2 x 0.5) deg2 for ~25 hours • DEEP2 survey: optical redshift survey by the Keck Telescope, ~50,000 redshifts 0.7<z<1.3 • Cross-correlation of HI & optical, probing 0.53 < z < 1.1 • Spatial resolution: Beam FWHM ~ 15’ => 9 h-1Mpc at z~0.8 • Spectral resolution ~ 24 kHz, rebinned to ~500 kHz => 2 h-1Mpc • Resolution element ~ (9 h-1Mpc)3

  22. HI content at z=0.8Cross-correlating GBT HI & DEEP2 optical galaxies at z ~ 0.7-1.1 GBT radio continuum sources + HI GBT HI (after SVD foreground subtraction) DEEP2 density

  23. HI content at z=0.8Cross-correlating GBT HI & DEEP2 optical galaxies at z ~ 0.7-1.1 • Measure HI & optical cross-correlation on 9 Mpc (spatial) x 2 Mpc (redshift) comoving scales • HI brightness temperature on these scales at z=0.8: • T = 157 ± 42 μK • ΩHI r b = (5.5 ± 1.5) x 10-4 • Highest-redshift detection of HI in emission at 4-sigma statistical significance. Chang, Pen, Bandura, Peterson, in Nature 2010

  24. Work in Progress: HI auto-correlation at z=0.8Auto- & Cross-correlating GBT HI & zCOSMOS galaxies at z ~ 0.5-1.1 GBT radio continuum sources + HI GBT HI (after SVD foreground subtraction) zCOSMOSdensity

  25. Next Step: HI Power spectrum at z~1 Masui et al.

  26. HI BAO Experiment Prospects • HI Intensity Mapping Experiment: 40,000m2 collecting area, 100 hrs of observation - competitive to DETF stage III experiment Chang, Pen, Peterson, McDonald 2008

  27. 21cm at z~1: current status • HI cross-correlation (with DEEP2 optical galaxies): measured at z~0.8: abundant HI at z~1; HI traces large-scale structure • HI auto-correlation at z~0.8: GBT on zCOSMOS field • HI large-scale structure redshift-space distortion: 50 deg, 300 hrs at GBT, observation and data analysis in progress (caution: foreground, calibration issues..) • Looking to build a survey instrument for Baryon Acoustic Oscillation measurement (e.g.,Chang et al. 08, Wyithe & Loeb 08, Seo et al. 10): large collecting area, compact configuration, wide-field survey (~104 m2) covering 0.5<z<2.5 (400-900 MHz, df~0.5 MHz), resolution ~10’ (10 comoving Mpc)

  28. Conclusion • BAO is a powerful tool for precision measurement of dark energy properties • 21-cm line is a promising large-scale structure tracer at low redshifts, yielding BAO measurements • 21-cm would be a good probe of the observable universe.

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