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Observing Cosmic Dawn with the LWA-1

Observing Cosmic Dawn with the LWA-1. Jackie Monkiewicz Arizona State University. PIs: Judd Bowman (ASU), Greg Taylor (UNM) Jake Hartman (JPL) Jayce Dowell, Joe Craig (UNM) Steve Ellingson (Virginia Tech). The “ Dark Ages ” and Cosmic Dawn. Dark Ages: z = 1,100 to z~ 40

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Observing Cosmic Dawn with the LWA-1

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  1. Observing Cosmic Dawn with the LWA-1 Jackie Monkiewicz Arizona State University PIs: Judd Bowman (ASU), Greg Taylor (UNM) Jake Hartman (JPL) Jayce Dowell, Joe Craig (UNM) Steve Ellingson (Virginia Tech)

  2. The “Dark Ages” and Cosmic Dawn • Dark Ages: z = 1,100 to z~ 40 • matter-dominated • H & He are neutral • 1st structures collapsing • Cosmic Dawn: z = 40-20 • 1st stars & galaxies • 1st QSOs? • Early heating, reionization of small bubbles

  3. Cosmic Dawn project purpose: • Detect/constrain signal of 1st generation of stars in 21-cm absorption of hydrogen at z ~ 30 • REQUIRES: • Low frequency experiment, 10-100 MHz • LWA-1 • Long Integration time • Very accurate bandpass calibration • Novel beamforming techniques

  4. Cosmic Dawn in 21 cm: Seen against CMB: DTb = Ts – Tcmb Thermal History of IGM (Furlanetto 2006, Pritchard & Loeb 2010)

  5. Cosmic Dawn in 21 cm: DTb = Ts - Tcmb • 1st stars create absorption trough • Additional heating sources mitigate trough (Furlanetto 2006, Pritchard & Loeb 2010)

  6. +50 D B 0 ΔT21 (mK) E (Pritchard & Loeb 2010) −50 A −100 C 20 40 60 80 100 120 140 160 180 ν (MHz) Observing strategy: • REQUIREMENTS: • Very good bandpass calibration! • Looking for broad, shallow absorption trough • need > 104 S/N in any spectral channel • But only need ~10% accuracy in absolute power…

  7. Observing strategy: • STRATEGY: • Simultaneously observe bright calibrators • & dark (low Tsys) science field • 2 x 19.6 MHz beams on bright calibrator • 2 x 19.6 MHz beams on science field • 520 hours on-sky

  8. Observing Strategy -- COMPLICATION: • Frequency variation of beam shape couples of foreground structure to sidelobes • mistake sources drifting through sidelobes for 21-cm spectral features? 1.0 74 MHz 38 MHz 0.8 0.6 Relative gain 0.4 0.2 0.0 −15 −10 −5 0 5 10 15 Offset (degrees)

  9. Novel Beamforming Strategies: Mitigate potential foreground-frequency coupling of sidelobes: • Defocusing (e.g. gaussian smoothing) • Sidelobe steering • Nulling • Sidelobe shimmering • “Optimized” beam-forming • (account for mutual coupling of antennas)

  10. Work to date: • Learning the LWA Software Library! • (and PYTHON in general) • Phase-and-Sum Beamforming with TBN • Raster Mapping of TBN Beam (pseudo-beams)

  11. Phase-and-Sum Beamforming: • TBN data:narrow bandwidth ( < 100 kHz) • Commissioning scripts for TBN (J.Dowell): • (follows “Fun with TBN” memo, S. Ellingson) • 1. Fringe all antenna outlier stand #258 • (simpleFringe.py ) • Fringe stop on bright source --- Cyg A or flaring Sun • back out delay coefficients • (solveCoeffs.py) • Use array geometry to point beam • (formBeam.py)

  12. Phase-and-Sum Beamforming: Find bursting Sun produces much better coefficients than Cyg A --- not surprising?

  13. Raster Mapping: Use bright source in TBN data to map structure of sidelobes --- “Pseudo-beam”

  14. Raster Mapping – Variation with elevation Cyg A: -1 hour EL = 76 deg Transit EL = 83 deg -2 hours EL = 65 deg

  15. Cas A NCP -2 hours before Cyg A transit EL = 34 deg @ Cyg A transit EL = 34 deg @ Cyg A transit EL = 46 deg … What is going on in the North/Northeast during the Cyg A transit on Sept 21, 2011??

  16. PASI started recording Sept 23, 2011: http://www.phys.unm.edu/~lwa/lwatv/55827.mov

  17. Pseudo-beam Maps over full frequency range: Acquired TBN observations of 4 frequency groups: 87 MHz 80 MHz 73 MHz 71 MHz 64 MHz 57 MHz …corresponding to 4 DRX tunings for main Cosmic Dawn observations 55 MHz 48 MHz 41 MHz 39 MHz 32 MHz 25 MHz Beam 1 Tuning 1 Beam 2 Tuning 1 Beam 1 Tuning 2 Beam 2 Tuning 2

  18. Test our Beamforming Strategies: Which is the “quickest and dirtiest”? • Defocusing (e.g. gaussian smoothing) • Sidelobe steering • Nulling • Sidelobe shimmering • “Optimized” beam-forming • (account for mutual coupling of antennas)

  19. Test our Beamforming Strategies: Which is the “quickest and dirtiest”? • Defocusing (e.g. gaussian smoothing) • Sidelobe steering • Nulling • Sidelobe shimmering • “Optimized” beam-forming • (account for mutual coupling of antennas)

  20. Pseudo-beam Maps over full frequency range: Apply some of our novel beam-forming strategies Defocusing is simplest, fastest  apply Gaussian to antenna gains  \ Acquire raster maps of customized DRX beams, compare with TBN predictions, confirm shape

  21. LWA-OCD Project Outputs: • Beamforming: • Detailed measurements of beam • Strategies for custom beamforming • Deep integrations: • Very high S/N spectra of bright calibrators • Very high S/N spectra of diffuse Galaxy • (including high-level H recombination lines) • Serendipitous radio transients • Lots of opportunity for RFI mitigation! • Detection/contraints on First Light absorption trough. END

  22. RFI environment at LWA:

  23. The “Dark Ages” and Cosmic Dawn z = redshift (decreases with increasing time) z =∞ z = 0

  24. The “Dark Ages” and Cosmic Dawn

  25. Wouthuysen-Field Effect:

  26. Phase-and-sum Beamforming: • Use bright source to back out coefficients • Only works for narrow (< 10 KHz bandwidth) • insensitive to 2p offsets Delay-and-sum Beamforming: • Do phase-and-sum over full LWA frequency range • Solve for true delays for each antenna

  27. System noise for LWA: From Pihlstrom, 2012, internal memo

  28. Acronyms:

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