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Baryon Acoustic Oscillations in the Lyman-α Forest of High Redshift Quasars

  • Author(s): Margala, Daniel
  • Advisor(s): Kirkby, David
  • et al.
Creative Commons 'BY' version 4.0 license

One of the main goals of the third generation of the Sloan Digital Sky Survey (SDSS) Baryon Oscillation Spectroscopic Survey (BOSS) is to measure the baryon acoustic oscillation (BAO) scale in the Lyman-α forest from observations of high-redshift (z > 2) quasars. The transmitted flux fraction in the forest provides a measure of the neutral hydrogen density along the line of sight that can be used to infer the clustering of the underlying dark matter distribution. Measurements of the BAO scale constrain the expansion history of the universe and can be used to infer the characteristics of dark energy. During the period 2009-14, the BOSS observed ~ 150,000 (z > 2) quasars from a total sky area of 10,400 square degrees.

I present a model for spectrophotometric calibration errors these observations of quasars and describe the correction procedure we have developed and applied to this sample. Calibration errors are primarily due to atmospheric differential refraction and guiding offsets during each exposure. The corrections potentially reduce the systematics for any studies of BOSS quasars, including the measurement of baryon acoustic oscillations using the Lyman-α forest. The model suggests that, on average, the observed quasar flux in BOSS is overestimated by ~ 19% at 3600 Å and underestimated by ~ 24% at 10,000 Å. In addition, a new method for simultaneously fitting a universal quasar continuum along with observing frame systematics is discussed. I also describe the sub-sampling method used to estimate the correlation function of the matter density tracer field and demonstrate this method using a new multithreaded software package designed to efficiently process pixel-pairs. The technique used to fit cosmological models to the estimated correlation function is summarized as well.

The BOSS BAO observations using the SDSS DR12 sample yield measurements of DH(z)/rd = 9.1 ± 0.3 and DM(z)/rd = 37.8 ± 2.1 at z = 2.34. These measurements represent a 1-2σ tension with the prediction from a flat ΛCDM model with Planck best-fit parameters.

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