Astronomy at 100 MHz

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Astronomy at 100 MHz HI-z vs ZZ Top
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Pre-WMAP
6.2
alter
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Gnedins simulation of Reionization
http//casa.colorado.edu/gnedin/GALLERY/
log(mean intensity of ionizing flux)
log(Neutral fraction)
log(density)
log T
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MAP
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MAP Result
Z 17 4
6.2
alter
???
Rules out WDM
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.. ionized
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Time scales for Recombination
t n /R
recomb
e
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Time scales for Recombination in IGM
t n /R
recomb
e
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Time scales for Recombination
t n /R
recomb
e
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R. Cen 2 Reionisations
Z 20 15 10 8
7 6
cold HI
warm HI
HII
HII
Pop III stars _at_ 500 Solar mass
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LOFAR and SKA
distributed star formation
Quasar
10 arcmin
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Foregrounds - Galactic synchrotron
- Discrete sources -
R.F.I.
log TB
TB f-2.6
180 K
180 MHz
log Frequency
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74 MHz x 6
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WMAP result
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Galactic / CMB separation
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TE Spectrum at low l
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The Z20 Expt
JR, FB, et al
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Barnbaum Bradley 1998
FM band in NRQZ Green Bank, WV
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A. Chippendale 3 feb 2003
Mileura Station min/median/max10 hrs _at_ 1 min
intervalsAzimuth 30 deg3kHz bandpass average
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RFI Subtraction with a reference horn

• origins in Int-Mit group at CSIRO ATNF
• illustrations from Parkes Telescope (Jon Bell et
  al.)

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gAS
g1I
Rx
Cross Correlation
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R F I
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Reference Antenna
I(t) S ha(t) io(t-ta)
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Reference Antenna
I
I(f) (S Ga(f) e-i2p taf ) Io(f)
G(f) Io(f)
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Cross correlation single polarization feed with
2 reference signals
1. Pol A
G1 G4 Io2
3. Ref 1
G3 G4 Io2
4. Ref 2
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Cross correlation single polarization feed with
2 reference signals
1. Pol A
G1 G4 Io2
C14
3. Ref 1
C34
G3 G4 Io2
4. Ref 2
G1
G1 G4 Io2

G3
G3 G4 Io2
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Practical Application Auto-Correlation
Spectrometer
Power Spectrum P(f)
S
gA2S2
g12 I2
A/C spectrometer
I
g12 I2
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Cross correlation single polarization feed with
2 reference signals
1. Pol A
G1 G3 Io2
C13
G1 G4 Io2
C14
3. Ref 1
C34
G3 G4 Io2
4. Ref 2
C13(f) C14(f) C34(f)
A/C Spectrum Contamination
g12 I2
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Cross correlation dual polarization feed with 2
reference signals
1. Pol A
C13
G1 G3 Io2
2. Pol B
C14
G1 G4 Io2
C23
G2 G3 Io2
C24
G2 G4 Io2
3. Ref 1
C34
G3 G4 Io2
4. Ref 2
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Raw Dynamic Spectra
Time
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Pol A
Pol B
frequency
Canceled Dynamic Spectra
Time
Non-Toxic to celestial signals
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Spectral Domain Contamination the VOLTAGE
spectrum
Estimate g1(f) I(f) X13(f) g3(f) I(f)
Time Domain Contamination
Effectively FIR filter coefficients
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FIR Coefficients
Delay 0.1ms steps

Time 0.1 sec steps
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Pol A
Pol B
using Ref. 3
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Dynamic Pulsar Spectra
Pol. B
Pol. A
Phase
Frequency
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Cancellation Applied
Dynamic Pulsar Spectra
Pol. B
Pol. A
Phase
Frequency
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Time Domain Contamination
P(t) g12 I(t) 2 g1I(t) 3
g1I(t) 4
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Time Domain Contamination
PI(t) g12 I(t) 2 g1I(t) 3
g1I(t) 4
( x13(t) N3 ) ( x14(t) N4 )
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Passband Normalization Applied
Dynamic Pulsar Spectra
Pol. B
Pol. A
Phase
Frequency
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Total Power Spectra
Ref B
Ref A
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Ref B
Raw Cross- correlation Spectra
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Ref B
Corrected Cross- correlation Spectra
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Steve Ellingson 17 Dec 1999
A Variation on the Ekers-Sault Correlation
Idea
Cross- correlation matrix
Eigen decomposition
Partition
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Twelve Eigenvalue Spectra
Frequency Channels
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Twelve Eigenvalue Spectra
Frequency Channels
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Eigenvector Spectra for one channel
(amplitudes of complex coefficients)

Frequency Channels
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Conclusions

• complications of multi-path are contained in
• complex gains G(f)
• adaptive filtering with correlation functions
• preserves phase information.
• equivalent to subtraction of the
  voltage waveform

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Applied RFI ID and subtraction
1. New 50cm Rx
2. 74 MHz
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ZZ Top

• when yer movin down the road,
• in yer V-8 foad,
• a shine on yer boots,
• and yer sideburns low