[Paper Review] Baryon Acoustic Oscillation detections from the clustering of massive halos and different density region tracers in TianNu simulation

Yu Liu, Liang Yu+4 more|arXiv (Cornell University)|Dec 4, 2017

Galaxies: Formation, Evolution, Phenomena8 references3 citations

TL;DR

This study uses the TianNu N-body simulation to investigate baryon acoustic oscillation (BAO) detections via Delaunay triangulation (DT) voids as tracers of low- and high-density regions. It demonstrates that BAO peak intensities are enhanced by an order of magnitude when using low-density region tracers (voids) compared to mock galaxies, with optimal detection at a void radius of ~34 Mpc/h.

ABSTRACT

The Baryon Acoustic Oscillations (BAO) refer to the ripples of material density in the Universe. As the most direct density tracers in the universe, galaxies have been commonly used in studies of BAO peak detection. The spatial number density of galaxies, to a certain extent, reflects the distribution of the material density of our Universe. Using galaxies as matter tracers, we can construct more overlapping empty spheres (DT voids) than the matter tracers, via Delaunay Triangulation technique. We show that their radii excellently reflect the galaxy number density round them, and they can serve as reliable different density region tracers. Using the data from an unprecedented large-scale $N$-body simulation "TianNu", we conduct some fundamental statistical studies and clustering analysis of the DT voids. We discuss in detail the representative features of two-point correlation functions of different DT void populations. We show that the peak, the position of which corresponds to the average radius of data samples, is the most representative feature of the two-point correlation function of the DT voids. In addition, we also construct another voids, the disjoint voids, and investigate their some statistical properties and clustering properties. And we find that the occupied space of all disjoint voids accounts for about $45\%$ of the volume of the simulation box, regardless of the number density of mock galaxies. We also investigate the BAO detections based on different tracers, i.e. mock galaxies, low-density region tracers, and high-density region tracers respectively. Our results show that BAO intensities detected by low/high-density region tracers are enhanced significantly compared to the BAO detection by mock galaxies, for the mock galaxy catalogue with the number density of $7.52 imes10^{-5}$ $h^3$ Mpc$^{-3}$.

Motivation & Objective

• To explore the clustering properties of Delaunay triangulation (DT) voids as tracers of cosmic density fields in the TianNu N-body simulation.
• To assess the effectiveness of DT voids and disjoint voids as low- and high-density region tracers in large-scale structure analysis.
• To compare BAO detection performance across mock galaxies, low-density tracers (DT voids), and high-density tracers (small DT voids).
• To identify optimal void radius cuts that maximize BAO signal strength in different density regimes.
• To evaluate the potential of DT voids as high-order statistics tools for probing neutrino effects on large-scale structure formation.

Proposed method

• Construct DT voids using Delaunay triangulation on mock galaxy distributions from the TianNu simulation, where each void is the circumsphere of a tetrahedron of galaxies with no other galaxies inside.
• Define low- and high-density region tracers based on the radii of DT voids: large voids trace low-density regions, small voids trace high-density regions.
• Compute two-point correlation functions (2PCF) for different DT void populations to analyze clustering features and locate BAO peaks.
• Apply Gaussian Process Regression (GPR) to fit 2PCFs of mock galaxies and void tracers to compare BAO signal intensities quantitatively.
• Investigate the statistical properties of disjoint voids (non-overlapping spheres) derived from overlapping DT voids to assess volume coverage and density dependence.
• Use the simulation’s high dynamic range and large volume to perform robust statistical analysis, especially on void size distributions and their correlation with local galaxy number density.

Experimental results

Research questions

• RQ1 How do the clustering properties of DT voids correlate with the underlying galaxy number density?
• RQ2 Can DT voids serve as reliable tracers of low- and high-density regions in the cosmic web?
• RQ3 What is the optimal void radius cut that maximizes BAO signal detection in low- and high-density regimes?
• RQ4 How do BAO peak intensities compare between mock galaxies and low/high-density region tracers?
• RQ5 To what extent does the volume occupied by disjoint voids depend on the number density of mock galaxies?

Key findings

• The peak position in the two-point correlation function of DT voids strongly correlates with the average void radius, making it a robust indicator of the underlying density field.
• Despite significant overlap, DT void radii reliably reflect the local galaxy number density, validating their use as density tracers.
• The total volume occupied by disjoint voids remains approximately 45% of the simulation box volume, independent of mock galaxy number density.
• For a mock galaxy number density of $7.52 \times 10^{-5} \, h^3 \, \text{Mpc}^{-3}$, the BAO peak intensity is enhanced by an order of magnitude when using low-density region tracers (DT voids) compared to mock galaxies.
• The optimal void radius cut for maximizing BAO signal in low-density tracers is $\sim 34 \, \text{Mpc}/h$.
• For high-density region tracers (small voids), the BAO signal increases with decreasing void radius but is limited by rising noise due to reduced sample size.