Mikkel Stockmann, MSc defense – University of Copenhagen

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Mikkel Stockmann, MSc defense


Title: Counting Holes in the Universe

Supervisors: Signe Riemer-Sørensen (U. Norway), Tamara Davis (U Queensland), Steen Hansen (DARK)


The matter in the Universe is distributed in web-like filaments with large regions of empty spaces in between, called voids. Recent N-body simulations by Villaescusa-Navarro et al. (2011) show a relation between the number of voids and the currently unknown mass of the neutrino, the lightest standard model particle. We were inspired by the results to investigate whether this effect is measurable in observational data. Since voids per definition contain very little matter, they are difficult to measure and can instead be classified from the empty regions between the patterns of the matter distribution. The matter distribution can be established from hydrogen clouds shadowing quasars that are among the most luminous light sources in the Universe.

We investigate the possibility of counting the number of voids, in UVES (VLT) high resolution quasar spectra (2 ≤ z ≤ 5), interpreted as the space between the Lyman-α absorption lines, in order to perform the first void count on real quasar data. From artificial mock spectra, I develop an automatic void counting method that enables us to make a statistical void count. To avoid subjective bias we determine our coding selection criteria from a subsample of 50 quasar spectra before running a blind analysis on the remaining quasar sample. We produce the to date first statistical void count comparison between simulated and observed quasar spectra along line of sight. We find an observed void count offset from the number of voids in simulation but to conclude any further we must increase our number statistics using the HIRES (Keck) data sample.

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