ترغب بنشر مسار تعليمي؟ اضغط هنا

A reanalysis of quasar absorption spectra results suggesting a spatial gradient in values of the fine-structure constant

130   0   0.0 ( 0 )
 نشر من قبل Julian Berengut
 تاريخ النشر 2012
  مجال البحث فيزياء
والبحث باللغة English




اسأل ChatGPT حول البحث

We statistically analyse a recent sample of data points measuring the fine-structure constant alpha (relative to the terrestrial value) in quasar absorption systems. Using different statistical techniques, we find general agreement with previous authors that a dipole model is a well-justified fit to the data. We determine the significance of the dipole fit relative to that of a simple monopole fit, discuss the consistency of the interpretation, and test alternate models for potential variation of alpha against the data. Using a simple analysis we find that the monopole term (the constant offset in (delta alpha)/alpha) may be caused by non-terrestrial magnesium isotope abundances in the absorbers. Finally we test the domain-wall model against the data.



قيم البحث

اقرأ أيضاً

The brightest southern quasar above redshift $z=1$, HE 0515$-$4414, with its strong intervening metal absorption-line system at $z_{abs}=1.1508$, provides a unique opportunity to precisely measure or limit relative variations in the fine-structure co nstant ($Deltaalpha/alpha$). A variation of just $sim$3 parts per million (ppm) would produce detectable velocity shifts between its many strong metal transitions. Using new and archival observations from the Ultraviolet and Visual Echelle Spectrograph (UVES) we obtain an extremely high signal-to-noise ratio spectrum (peaking at S/N $approx250$ pix$^{-1}$). This provides the most precise measurement of $Deltaalpha/alpha$ from a single absorption system to date, $Deltaalpha/alpha=-1.42pm0.55_{rm stat}pm0.65_{rm sys}$ ppm, comparable with the precision from previous, large samples of $sim$150 absorbers. The largest systematic error in all (but one) previous similar measurements, including the large samples, was long-range distortions in the wavelength calibration. These would add a $sim$2 ppm systematic error to our measurement and up to $sim$10 ppm to other measurements using Mg and Fe transitions. However, we corrected the UVES spectra using well-calibrated spectra of the same quasar from the High Accuracy Radial velocity Planet Searcher (HARPS), leaving a residual 0.59 ppm systematic uncertainty, the largest contribution to our total systematic error. A similar approach, using short observations on future, well-calibrated spectrographs to correct existing, high S/N spectra, would efficiently enable a large sample of reliable $Deltaalpha/alpha$ measurements. The high S/N UVES spectrum also provides insights into analysis difficulties, detector artifacts and systematic errors likely to arise from 25-40-m telescopes.
287 - J. B. Whitmore 2014
We present a new `supercalibration technique for measuring systematic distortions in the wavelength scales of high resolution spectrographs. By comparing spectra of `solar twin stars or asteroids with a reference laboratory solar spectrum, distortion s in the standard thorium--argon calibration can be tracked with $sim$10 m s$^{-1}$ precision over the entire optical wavelength range on scales of both echelle orders ($sim$50--100 AA) and entire spectrographs arms ($sim$1000--3000 AA). Using archival spectra from the past 20 years we have probed the supercalibration history of the VLT--UVES and Keck--HIRES spectrographs. We find that systematic errors in their wavelength scales are ubiquitous and substantial, with long-range distortions varying between typically $pm$200 m s$^{-1}$ per 1000 AA. We apply a simple model of these distortions to simulated spectra that characterize the large UVES and HIRES quasar samples which previously indicated possible evidence for cosmological variations in the fine-structure constant, $alpha$. The spurious deviations in $alpha$ produced by the model closely match important aspects of the VLT--UVES quasar results at all redshifts and partially explain the HIRES results, though not self-consistently at all redshifts. That is, the apparent ubiquity, size and general characteristics of the distortions are capable of significantly weakening the evidence for variations in $alpha$ from quasar absorption lines.
67 - Yevgeny V. Stadnik 2020
Quasar absorption spectral data indicate the presence of a spatial gradient in the electromagnetic fine-structure constant $alpha$ on cosmological length scales. We point out that experiments with accelerometers, including torsion pendula and atom in terferometers, can be used as sensitive probes of cosmological spatial gradients in the fundamental constants of nature, which give rise to equivalence-principle-violating forces on test masses. Using laboratory data from the Eot-Wash experiment, we constrain spatial gradients in $alpha$ along any direction to be $| boldsymbol{ abla} alpha / alpha | < 6.6 times 10^{-4}~(textrm{Glyr})^{-1}$ at $95%$ confidence level. Our result represents an order of magnitude improvement over laboratory bounds from clock-based searches for a spatial gradient in $alpha$ directed along the observed cosmological $alpha$-dipole axis. Improvements to accelerometer experiments in the foreseeable future are expected to provide sufficient sensitivity to test the cosmological $alpha$-dipole seen in astrophysical data.
A new and automated method is presented for the analysis of high-resolution absorption spectra. Three established numerical methods are unified into one artificial intelligence process: a genetic algorithm (GVPFIT); non-linear least-squares with para meter constraints (VPFIT); and Bayesian Model Averaging (BMA). The method has broad application but here we apply it specifically to the problem of measuring the fine structure constant at high redshift. For this we need objectivity and reproducibility. GVPFIT is also motivated by the importance of obtaining a large statistical sample of measurements of $Deltaalpha/alpha$. Interactive analyses are both time consuming and complex and automation makes obtaining a large sample feasible. In contrast to previous methodologies, we use BMA to derive results using a large set of models and show that this procedure is more robust than a human picking a single preferred model since BMA avoids the systematic uncertainties associated with model choice. Numerical simulations provide stringent tests of the whole process and we show using both real and simulated spectra that the unified automated fitting procedure out-performs a human interactive analysis. The method should be invaluable in the context of future instrumentation like ESPRESSO on the VLT and indeed future ELTs. We apply the method to the $z_{abs} = 1.8389$ absorber towards the $z_{em} = 2.145$ quasar J110325-264515. The derived constraint of $Deltaalpha/alpha = 3.3 pm 2.9 times 10^{-6}$ is consistent with no variation and also consistent with the tentative spatial variation reported in Webb et al (2011) and King et al (2012).
التعليقات
جاري جلب التعليقات جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
mircosoft-partner

هل ترغب بارسال اشعارات عن اخر التحديثات في شمرا-اكاديميا