A new result on space-time variation of α – part B
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Transcript of A new result on space-time variation of α – part B
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A new result on space-time variation of α –
part B
Julian King (UNSW)Collaborators: John Webb (UNSW),
Victor Flambaum (UNSW)Michael Murphy (Swinburne)
Bob Carswell (IOA Cambridge)…and others
•
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The previous status of αΔα
/α (1
0-5)
• Current largest sample of quasar absorber constraints on Δα/α come from Murphy et al (2004) from Keck/HIRES• Found that Δα/α = ( -0.57 ± 0.11 ) x 10-5
• Effect larger at z>1 ??• Obvious question: what would a different telescope find?
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The VLT sample
The goal:• To use archive spectra from UVES (Ultraviolet and Visual Echelle
Spectrograph) on the VLT in Chile to try to confirm (or dispute) the Keck results
The method:• In the same manner as the previous Keck results, we fit Voigt
profiles to the quasar profiles and determine Δα/α• We derive a sample of 153 final quasar absorbers = 153 x Δα/α• We have verified that our uncertainties are correct using Markov
Chain Monte Carlo methods• Other improvements in technique (Levenberg-Marquardt
algorithm, determining number of components using Akaike Information Criterion, robust statistical methods)
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Δα/α vs redshift – VLT sample
Weighted mean:Δα/α = (0.23 ± 0.12) x 10-5
(after increasing error bars to account for χ2
ν=1.78)
compare with Murphy et al (2004):
Δα/α = (-0.57 ± 0.11) x 10-5
Error bars increased by 0.9 x 10-5
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Δα/α vs redshift – comparison with Keck
VLT + Keck
Keck
VLT
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VLT – Correlation with declination?
Declination is equivalent to
latitude
2.1σcorrelation
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Correlation with declination after adding in Keck data
VLTKeck
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Δα/α data for different sightlines
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4.1σ evidence for a Δα/α dipole from VLT + Keck
Δα/α = c + A cos(θ)
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The Keck & VLT dipoles point in the same direction
VLT Keck Combined
20 degreesp = 0.05
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Low and high redshift cuts are consistent in direction......but the effect is larger at high redshift...
z > 1.6 z < 1.6 Combined
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...so add in a simple time relationship
Δα/α = c + A t cos(θ)
4.1σ evidence
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What next?
• Although the results appear consistent, important to look for systematics (next talk!)• And of course... More observations!
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Could increase signal through high-declination observations