low frequency wide field astronomy with paper precision array to probe the epoch of reionization
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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

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.)‏

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

slide4

The new [epoch of reionization] map may carry more information than even the cosmic microwave background radiation.

- Avi Loeb, Scientific American, Nov. 06

seeing in the dark
Seeing in the Dark

“Spin flip” transition of hydrogen at 21 cm wavelength, unmitigated by dust in the Galaxy

NRAO/AUI

seeing in the dark1
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

the story s o far
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

the paper approach
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

the paper approach1
The PAPER Approach

21-cm Power Spectrum

Point Sources/1000

PWA-128 Uniform

PWA-128 Gaussian

Synchrotron/1000

the paper approach2
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
paper 16gb
PAPER-16GB
  • Picture of array and antennas
paper 16gb1
PAPER-16GB
  • Block diagram
  • Deployments (set up for position fitting)
  • Configuration decisions
interferometry 101
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!
interferometry 1011
Interferometry 101
  • Position fitting phase plots
  • Preliminary positions results
the next challenge
The Next Challenge…

http://madrigal.haystack.mit.edu/models/IRI/index.html

http://radiojove.gsfc.nasa.gov

the ionosphere in interferometry
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.

the ionosphere in interferometry1
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.

the ionosphere in interferometry2
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.

modeling the ionosphere
Modeling the Ionosphere
  • Simple spherical model and eqn
  • Compare results to data for Cas
modeling the ionosphere1
Modeling the Ionosphere
  • Then talk about irregularities and first pass at that
  • Next is to model image effects and try different irregularities
parallel path through the data
Parallel Path through the Data
  • Continue w/ 16 and add outriggers b/c effect exaggerated
  • But also improve resolution for point source removal
outriggers
Outriggers
  • Technical issues (power, signal, solving positions)
  • So step out!
outriggers1
Outriggers
  • Surveyed map and pictures from that
next step green bank
Next Step… Green Bank
  • Expand model and bring together model and data
  • Other stability experiments?
next step australia
Next Step… Australia
  • 32 elements deployment in the fall w/ pic of groundscreens in GB ready to go…
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