Presented by: Tabitha Voytek

1. From Dark to Light Hydrogen and the First Stars
Tabitha Voytek, Carnegie Mellon University
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SCI-HI Project Collaborators: Jeff Peterson (CMU), Aravind Natarajan (CMU/Pitt)
*Omar Lopez-Cruz (INAOE), Jose-Miguel Jauegui-Garcia (INAOE), Edgar Castillo (INAOE)
*Other future collaborators in Mexico

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Background
Instrument
Deployment
Analysis
Results
Improvements

3. Observations with the SCI-HI experiment focus on first star formation during the Cosmic Dawn.
Image: http://www.nasa.gov/mission_pages/planck/multimedia/pia16876b.html
SCI-HI Observations
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Background Deployments Results
Instrument Analysis Improvements

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Background

5. All 21-cm observations are made using Hyperfine splitting of the ground state of hydrogen.
1s 1S1/2
ΔE → 1420 MHz → 21-cm
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Background Deployments Results
Instrument Analysis Improvements

6. Hyperfine splitting is energy differentiation caused by the spin alignment of the proton and electron.
Image from: http://aliceingalaxyland.blogspot.com/2009/04/mini-spinni-antics-of-atoms-in-space.html
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Background Deployments Results
Instrument Analysis Improvements

7. Neutral hydrogen (HI) gas can be found in the Interstellar and Intergalactic Medium (IGM).
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Hydrogen 21-cm Emission Contours for M51
Image from: http://www.haydenplanetarium.org
Background Deployments Results
Instrument Analysis Improvements

8. All-sky 21-cm spectrum experiments measure the average
redshift evolution of HI gas in the IGM.
Image: Pritchard and Loeb, Nature, 2010
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1/ 2 T (1 )(1 z)
s
initial
T
T
b space    
Background Deployments Results
Instrument Analysis Improvements
obs
emit obs z

 


9. In particular, the SCI-HI experiment focuses on the all-sky averaged signal during the Cosmic Dawn (z~20).
Image: Pritchard and Loeb, Nature, 2010
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Background Deployments Results
Instrument Analysis Improvements
SCI-HI Measures Here

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Instrument

11. Three primary components were considered in designing the SCI-HI instrument.
Antenna
Working Frequencies: 40-130 MHz
RF Electronics
Switch, amplifiers, filters and cables
Computer
Analog to Digital Conversion and Fourier Transform
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Background Deployments Results
Instrument Analysis Improvements

12. The SCI-HI antenna went through several different iterations before settling on the HIbiscus design.
Trombone Antenna
HIbiscus Antenna v1
HIbiscus Antenna v2
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Background Deployments Results
Instrument Analysis Improvements

13. Data was collected with the preliminary SCI-HI instrument in June 2013 on Isla Guadalupe.
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Background Deployments Results
Instrument Analysis Improvements

14. At the time, the instrument had a single antenna and relied on 12V car batteries for DC power.
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Background Deployments Results
Instrument Analysis Improvements

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Deployment

16. Terrestrial radio frequency interference (RFI) is a significant problem in radio astronomy.
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Background Deployments Results
Instrument Analysis Improvements

17. We evaluated current and potential experiment sites for their RFI environmental quality.
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Background Deployments Results
Instrument Analysis Improvements

18. At each site, quality was investigated using a portable antenna and spectrum analyzer.
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Algonquin
Guadalupe
Background Deployments Results
Instrument Analysis Improvements

19. We chose to deploy SCI-HI at Isla Guadalupe based upon the excellent RFI environment.
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FM band as measured with the SCI-HI instrument
Background Deployments Results
Instrument Analysis Improvements

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Analysis

21. Data collection includes both the sky signal and calibration source signals.
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Background Deployments Results
Instrument Analysis Improvements

22. Sky signals collected with the HIbiscus antenna are
dominated by the Milky Way Galaxy.
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Background Deployments Results
Instrument Analysis Improvements

23. This Milky Way Galaxy signal varies over each day due to the antenna beam sky coverage.
Daily Signal Variation at 70 MHz
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Background Deployments Results
Instrument Analysis Improvements

24. Calibration utilizes the Milky Way Galaxy foreground model and daily mean/variance.
Beam Averaged Sky Temperature: 푇퐺푆푀푡,휐= 푑Ω 퐺푆푀휃,휙,휐퐵(휃−휃0푡,휙−휙0푡,휐) 푑Ω 퐵(휃−휃0푡,휙−휙0푡,휐)
GSM Model comes from de Oliveira-Costa et al. (2008)
χ² Fitting: 휒2휐= Δ푇푚푒푎푠푡,휐−Δ푇퐺푆푀푡,휐2 푡
Daily Mean Subtraction: Δ푇푚푒푎푠푡,휐=푇푚푒푎푠푡,휈−푇푚푒푎푠퐷퐴푌(휐) Δ푇퐺푆푀푡,휐=푇퐺푆푀푡,휈−푇퐺푆푀퐷퐴푌(휐)
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Background Deployments Results
Instrument Analysis Improvements

25. KΔGSM calibration is most successful when a full day of data is collected.
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Background Deployments Results
Instrument Analysis Improvements

26. Example KΔGSM Mean and Fit
After calibration, foreground removal was done using a simple polynomial fitting and subtraction.
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푙표푔10푇퐺푀(휐)= 푎푘 푙표푔10( 휐 70 푀퐻푧 ) 푘 푛 푘=0
푇푟푒푠휐=푇푚푒푎푠퐷퐴푌휐 −푇퐺푀(휐)
Daily Fit:
Daily Residuals:
Background Deployments Results
Instrument Analysis Improvements

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Results

28. Preliminary data collection in June 2013 gave good results, but further improvements are necessary.
KJNC Calibrated
KΔGSM Calibrated
Predicted 21-cm Signal Models
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Background Deployments Results
Instrument Analysis Improvements

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Improvements

30. Problem: DC battery is unreliable. Solution: Replace battery with an AC gas generator.
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Background Deployments Results
Instrument Analysis Improvements

31. Problem: DC battery is unreliable. Solution: Replace battery with an AC gas generator.
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Background Deployments Results
Instrument Analysis Improvements

32. Problem: Antenna frequency range is too small. Solution: Build multiple scaled antennae.
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70 MHz Scale
100 MHz Scale
Background Deployments Results
Instrument Analysis Improvements

33. Problem: Self-generated RFI seen in data. Solution: Double Faraday cage for computer.
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Double Faraday Cage
Computer inside inner Faraday Cage
Background Deployments Results
Instrument Analysis Improvements

34. Problem: Isla Guadalupe still not remote enough. Solution: Find more remote sites.
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Time Series of the FM band for June 1st, 2013 data
Time Average of the FM band for June 1st, 2013
Background Deployments Results
Instrument Analysis Improvements

35. Problem: Isla Guadalupe still not remote enough. Solution: Isla Socorro/Clarion and/or Marion Island.
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Guadalupe
Socorro
Clarion
Marion Island
Background Deployments Results
Instrument Analysis Improvements

36. With these changes, the SCI-HI experiment will help us better understand the first stars.
Foregrounds
Current Best Results (KΔGSM)
Predicted 21-cm
Models
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Background Deployments Results
Instrument Analysis Improvements

37. S C I – H I
Sonda Cosmológica de las Islas para la Detección de Hidrógeno Neutro
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