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A new result on space-time variation of alpha – Part C

A new result on space-time variation of alpha – Part C. John Webb, School of Physics, University of New South Wales , Australia. Group members as per Michael Murphy’s first slide. Two interesting internal consistencies:

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A new result on space-time variation of alpha – Part C

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  1. A new result on space-time variation of alpha – Part C John Webb, School of Physics, University of New South Wales, Australia Group members as per Michael Murphy’s first slide

  2. Two interesting internal consistencies: Keck and VLT dipole positions agree (although errors fairly large). Independent samples, different data reduction procedures, different instruments and telescopes. High and low redshift dipole sky positions (using combined dataset) also agree - perhaps even more compelling because different species are used at low and highredshift – and different transitions respond differently to the same change in a. And an interesting robustness indication: Rather than increasing the statistical error bars to force c2n = 1, we can instead iteratively trim the individualDa/apoints relative to the dipole model. How much do we have to trim to destroy the result? What are the key points which collectively suggest this result might be cosmological and not due to systematics?

  3. Highly exaggerated illustration of how transitions shift in different directions by different amounts – unique pattern

  4. Are a few high S/N outliers responsible for the signal, by chance? • Alternative to growing error bars • Robustness check – iterative trimming • Adopt statistical-only errors and iteratively clip most deviant point • How much data do we need to discard to remove the dipole and time dependence? • c2n = 1 reached when ~10% clipped • Linear time fit significance ~5s at c2n = 1 • Linear time fit significance stays above 4s until ~40% of data discarded • c2n = 1 reached when ~10% clipped • Dipole significance ~7s at c2n = 1 • Dipole significance stays above 4s until ~50% of data discarded

  5. Can we nevertheless find a systematic which can reproduce these? Two approaches: Identify all the systematics one can possibly think of and quantify them one by one Find a purely empirical approach which in principle measures both known and unknown simultaneously

  6. Alignment of quasar image on the spectrograph slit Ok Good Not nice Nasty

  7. VLT/UVES vs. Keck/HIRES: Time HIRES: Single arm, single chip (pre-Aug.'04) l[Å] 3000 5500 8000 Time UVES: Dual-arm, 3 chips l[Å] 3000 5500 8000

  8. VLT/UVES vs. Keck/HIRES: Time HIRES: Single arm, single chip (pre-Aug.'04) l[Å] 3000 5500 8000 Time Molaro et al. (A&A, 2008): UVES slits well aligned UVES: Dual-arm, 3 chips l[Å] 3000 5500 8000

  9. VLT/UVES vs. Keck/HIRES: Time HIRES: Visitor mode, follow object with ThAr Cal. Obj. Cal. Obj. l[Å] 3000 5500 8000 Time UVES: Service mode, ThAr at end of night Cal. Cal. Obj. Obj. l[Å] 3000 5500 8000

  10. 7 quasars observed on both Keck and VLT – a direct test of combined systematics Quasar Keck To Earth VLT

  11. Comparing Da/a for 14 absorption systems observed with both Keck and VLT

  12. Pairs of quasar observations on both Keck and VLT

  13. ~800 measurements, 7 quasar spectra observed on both Keck and VLT

  14. Same as previous plot but binned

  15. No systematic – standard laboratory frequencies: Worst-case systematic – Modify the laboratory frequency: Implementing the dv test

  16. Before and after No dv systematic applied With dv systematic

  17. Conclusions • The “raw” data might now be indicating both time and space variation of alpha. • The quasar pair test results represent an upper limit on any effect. They do not provide a "correction” to the raw results.  We do not expect this in the sample as a whole. • Nevertheless, if we do impose such an extreme effect on the whole raw dataset, it does not generate a solution in whichDa/ais constant. • Further, imposing the effect slightly diminishes the previous internal consistency in the data, as would be expected if the dipole is real. • Specifically, the significance of the dipole reduces (although still remains fairly significant) and we then also require a more significant monopole term (which may seem "unphysical"). • Finally, we have so far been unable to find a way of explaining the results in terms of any known (or even unknown) systematics.

  18. Further work • Need completely independent check. Meanwhile, continue with quasar spectroscopy – will double the existing sample within ~3 years • Also targeted observations: ? ? • Need more duplicate observations on both Keck and VLT • Also really need more H2 absorption systems. • Other combinations of lines, e.g. HI 21cm + neutral.

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