From Dark to Light: Hydrogen and the First Stars

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

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

3 Background Deployments Results

Instrument Analysis Improvements

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Background

All 21-cm observations are made using Hyperfine splitting of the ground state of hydrogen.

1s 1S1/2

ΔE → 1420 MHz → 21-cm



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



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


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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2/1)1)(1( zTs

initial

T

T

spaceb



obs

obsemitz

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



SCI-HI Measures Here

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Instrument

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



The SCI-HI antenna went through several different iterations before settling on the HIbiscus design.

Trombone Antenna HIbiscus Antenna v1 HIbiscus Antenna v2



Data was collected with the preliminary SCI-HI instrument in June 2013 on Isla Guadalupe.



At the time, the instrument had a single antenna and relied on 12V car batteries for DC power.



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Deployment

Terrestrial radio frequency interference (RFI) is a significant problem in radio astronomy.



We evaluated current and potential experiment sites for their RFI environmental quality.



At each site, quality was investigated using a portable antenna and spectrum analyzer.

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Algonquin Guadalupe



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



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Analysis

Data collection includes both the sky signal and calibration source signals.



Sky signals collected with the HIbiscus antenna are dominated by the Milky Way Galaxy.



This Milky Way Galaxy signal varies over each day due to the antenna beam sky coverage.

Daily Signal Variation at 70 MHz



Calibration utilizes the Milky Way Galaxy foreground model and daily mean/variance.

Beam Averaged Sky Temperature:

𝑇𝐺𝑆𝑀 𝑡, 𝜐 = 𝑑Ω 𝐺𝑆𝑀 𝜃, 𝜙, 𝜐 𝐵(𝜃 − 𝜃0 𝑡 , 𝜙 − 𝜙0 𝑡 , 𝜐)

𝑑Ω 𝐵(𝜃 − 𝜃0 𝑡 , 𝜙 − 𝜙0 𝑡 , 𝜐)

GSM Model comes from de Oliveira-Costa et al. (2008)

χ² Fitting:

𝜒2 𝜐 = Δ𝑇𝑚𝑒𝑎𝑠 𝑡, 𝜐 − Δ𝑇𝐺𝑆𝑀 𝑡, 𝜐2

𝑡

Daily Mean Subtraction:

Δ𝑇𝑚𝑒𝑎𝑠 𝑡, 𝜐 = 𝑇𝑚𝑒𝑎𝑠 𝑡, 𝜈 − 𝑇𝑚𝑒𝑎𝑠 𝐷𝐴𝑌(𝜐)

Δ𝑇𝐺𝑆𝑀 𝑡, 𝜐 = 𝑇𝐺𝑆𝑀 𝑡, 𝜈 − 𝑇𝐺𝑆𝑀 𝐷𝐴𝑌(𝜐)



KΔGSM calibration is most successful when a full day of data is collected.



Example KΔGSM Mean and Fit

After calibration, foreground removal was done using a simple polynomial fitting and subtraction.

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𝑙𝑜𝑔10 𝑇𝐺𝑀(𝜐) = 𝑎𝑘 𝑙𝑜𝑔10(𝜐

70 𝑀𝐻𝑧)𝑘

𝑛

𝑘=0

𝑇𝑟𝑒𝑠 𝜐 = 𝑇𝑚𝑒𝑎𝑠 𝐷𝐴𝑌 𝜐 − 𝑇𝐺𝑀(𝜐)

Daily Fit:

Daily Residuals:



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Results

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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Improvements

Problem: DC battery is unreliable. Solution: Replace battery with an AC gas generator.



Problem: DC battery is unreliable. Solution: Replace battery with an AC gas generator.



Problem: Antenna frequency range is too small. Solution: Build multiple scaled antennae.

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70 MHz Scale

100 MHz Scale



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



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



Problem: Isla Guadalupe still not remote enough. Solution: Isla Socorro/Clarion and/or Marion Island.

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Guadalupe

Socorro Clarion

Marion Island



With these changes, the SCI-HI experiment will help us better understand the first stars.

Foregrounds

Current Best Results (KΔGSM)

Predicted 21-cm Models



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

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From Dark to Light: Hydrogen and the First Stars

Engineering

scihi antenna

scihi experiment

preliminary scihi instrument

neutral hydrogen hi

portable antenna

single antenna

antenna beam sky coverage

sky signals