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Low Frequency, Wide-Field Astronomy with PAPER: Precision Array to Probe the Epoch of Reionization

Low Frequency, Wide-Field Astronomy with PAPER: Precision Array to Probe the Epoch of Reionization. Nicole Gugliucci Graduate Student, UVa /NRAO Advisor: Rich Bradley. Collaborators: D. Backer, A. Parsons, J. Manley, G. Foster, M . Wright, D. Werthimer , CASPER group (UCB),

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Low Frequency, Wide-Field Astronomy with PAPER: Precision Array to Probe the Epoch of Reionization

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  1. Low Frequency, Wide-Field Astronomy with PAPER:Precision Array to Probe the Epoch of Reionization Nicole Gugliucci Graduate Student, UVa/NRAO Advisor: Rich Bradley Collaborators: D. Backer, A. Parsons, J. Manley, G. Foster, M. Wright, D. Werthimer, CASPER group (UCB), C. Parashare, E. Mastrantonio,P. Klima (UVa/NRAO), C. Carilli, A. Datta, (NRAO/NMT) J. Aguirre, D. Jacobs (U. Colorado) , M. Lynch, D. Herne, T. Colegate (Curtin U.)‏

  2. Outline • What is the epoch of reionization? • The PAPER approach • Green Bank deployment • Early results • Ionosphere challenge • Future work

  3. What is the EoR? NASA/WMAP Team The universe was created in a Big Bang 13.7 billion years ago. 300,000 years later, protons and electrons first came together to create hydrogen and the Cosmic Microwave Background. Today, we see stars, galaxies, and clusters, and all of the hydrogen in intergalactic space is ionized. What happened in between?

  4. The new [epoch of reionization] map may carry more information than even the cosmic microwave background radiation. - Avi Loeb, Scientific American, Nov. 06

  5. Seeing in the Dark “Spin flip” transition of hydrogen at 21 cm wavelength, unmitigated by dust in the Galaxy NRAO/AUI

  6. Seeing in the Dark The 21 cm or 1.4 GHz transition marks a protected band for radio astronomy, due to the importance of hydrogen as an astronomical tracer. However, the hydrogen at the EoR is redshifted to a lower frequency. Doppler Shift + Expanding Universe -> most astronomical objects appear redshifted. The redshift (z) is related to the distance the object is from us and, more importantly, how far back in time we are looking! z = 0.1 was 1.3 billion years ago z = 1 was 7.7 billion years ago z = 7 was 12.9 billion years ago z = 1100 was time of CMB Machele Cable of Wake Forest Ned Wright's Cosmology Tutorial

  7. The Story So Far Gunn-Peterson trough at z=6.28 (Becker et al. 2001) indicates end of reionization; Lyman transitions opaque at neutral fraction ~ 10-2 - 10-3 WMAP (Spergel et al. 2007): power spectrum of TE mode of CMB polarization measures the optical depth of free electrons, indicating that if instantaneous, reionization would have occurred at z~10. Reionization occurs z ~ 6 - 14, redshifted to 100 – 230 MHz

  8. The PAPER Approach • Actual imaging of the neutral hydrogen will take many more times the sensitivity of current telescopes • Instead, measure power spectrum of the fluctuating signal at different redshifts, or different times • This is natural for an interferometer, which detects spatial frequencies Condon & Ransom Christian Deichert

  9. The PAPER Approach 21-cm Power Spectrum Point Sources/1000 PWA-128 Uniform PWA-128 Gaussian Synchrotron/1000

  10. The PAPER Approach • Staggered deployments – learn at each stage • Test and measure everything before we do science • antenna beam pattern • response of receivers, amplifiers, cable, etc. • digitization effects of correlator • Science and data quality drives instrumentation • Develop new methods of imaging to fit our needs: wide bandwidth and full sky without tracking

  11. PAPER-16GB • Picture of array and antennas

  12. PAPER-16GB • Block diagram • Deployments (set up for position fitting) • Configuration decisions

  13. Interferometry 101 • Need to calibrate the data for precise antenna positions, cable delays, and other effects to produce calibrated visibilities, or measurements at certain spatial frequencies • These visibilities are then deconvolved to produce a sky image. Note that the spatial frequency plane is not fully sampled!

  14. Interferometry 101 • Position fitting phase plots • Preliminary positions results

  15. The Next Challenge… http://madrigal.haystack.mit.edu/models/IRI/index.html http://radiojove.gsfc.nasa.gov

  16. The Ionosphere in Interferometry Kassim et al. (2007) defines the isoplanatic patch as more specifically as the region of with a phase difference less than one radian at a particular observing frequency Isoplanatic Patch Phase vs. Time for 3 Directions Work at the VLA at 74 MHz probed different ionospheric disturbances From Kitchin, Astrophysical Techniques Phase of three antennas relative to a central antenna during an approximately 8 hr observation of Vir A illustrating many of the ionospheric phenomena typically observed at the VLA.

  17. The Ionosphere in Interferometry Kassim et al. (2007) defines the isoplanatic patch as more specifically as the region of with a phase difference less than one radian at a particular observing frequency Isoplanatic Patch Phase vs. Time for Baseline Lengths Work at the VLA at 74 MHz probed different ionospheric disturbances From Kitchin, Astrophysical Techniques Same as previous except for two antennas at different distances along the same azimuth, indicating that to first order the phase effects of all the phenomena are proportional to baseline length.

  18. The Ionosphere in Interferometry Kassim et al. (2007) defines the isoplanatic patch as more specifically as the region of with a phase difference less than one radian at a particular observing frequency Isoplanatic Patch Position vs. Time for RA and Dec Work at the VLA at 74 MHz probed different ionospheric disturbances From Kitchin, Astrophysical Techniques Refraction (or apparent position wander in both right ascension and declination) of Virgo A over the same timescale as before, 8 hours.

  19. Modeling the Ionosphere • Simple spherical model and eqn • Compare results to data for Cas

  20. Modeling the Ionosphere • Then talk about irregularities and first pass at that • Next is to model image effects and try different irregularities

  21. Parallel Path through the Data • Continue w/ 16 and add outriggers b/c effect exaggerated • But also improve resolution for point source removal

  22. Outriggers • Technical issues (power, signal, solving positions) • So step out!

  23. Outriggers • Surveyed map and pictures from that

  24. Next Step… Green Bank • Expand model and bring together model and data • Other stability experiments?

  25. Next Step… Australia • 32 elements deployment in the fall w/ pic of groundscreens in GB ready to go…

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