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

•

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?

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)

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

Δα/α vs redshift – comparison with Keck

VLT + Keck

Keck

VLT

VLT – Correlation with declination?

Declination is equivalent to

latitude

2.1σcorrelation

Correlation with declination after adding in Keck data

VLTKeck

Δα/α data for different sightlines

4.1σ evidence for a Δα/α dipole from VLT + Keck

Δα/α = c + A cos(θ)

The Keck & VLT dipoles point in the same direction

VLT Keck Combined

20 degreesp = 0.05

Low and high redshift cuts are consistent in direction......but the effect is larger at high redshift...

z > 1.6 z < 1.6 Combined

...so add in a simple time relationship

Δα/α = c + A t cos(θ)

4.1σ evidence

What next?

• Although the results appear consistent, important to look for systematics (next talk!)• And of course... More observations!

Could increase signal through high-declination observations