The Size and Shape Dependence of the SDSS Galaxy Bispectrum

The Size and Shape Dependence of the SDSS Galaxy Bispectrum

ELSEVIER Article: https://www.sciencedirect.com/science/article/abs/pii/S1384107624001064

Highlights

1. We study the dependence of monopole bispectrum on all possible tringle shapes and sizes (within k range 0.075-0.434 Mpc-1)

2. Bispectrum corresponding to all triangles can be fitted with a single power law.

3. For the first time, we present a way to visualize the bispectrum corresponding to full triangle-parameter space (shape and size of triangle).

4. The SDSS samle (low redshift) can be modelled by using only two parameters, which are smoothing scale and linear bias instead of complicated HOD models. This fact is verified using mock samples from N-body simulations.

5. We studied the bispectrum of red and blue galaxies. The red galaxies exhibit higher bispectrum amplitude A than the blue galaxies for all possible triangle configurations. Red galaxies are old, and their larger bispectra indicate non-linear evolutionary interactions within their environments over time, resulting in their distribution being highly clustered and more biased than younger blue galaxies.

Introduction

Observations of the spatial distribution of galaxies enable us to study the large-scale structures (LSS) in the Universe. A variety of works (Sefusatti et al., 2009, Fergusson et al., 2012, Oppizzi et al., 2018, Shiraishi, 2019, Feldman et al., 2001, Liguori et al., 2010), and particularly the Planck 2018 results (Akrami et al., 2020), all indicate that the LSS originated from very small amplitude (linear) Gaussian primordial density perturbations. It is possible to entirely quantify the statistics of these primordial perturbations using the two-point correlation function or its Fourier counterpart the power spectrum. The subsequent amplification of these perturbations, through the process of gravitational instability (Peebles, 1980), is non-linear and the LSS ceases to be Gaussian (e.g. Fry, 1984, Fry, 1994, Bharadwaj, 1994). The three-point correlation function or its Fourier counterpart the bispectrum are the lowest order statistics which quantify the non-Gaussianity in the LSS (e.g. Fry and Seldner, 1982). The bispectrum, which refers to a closed triangle of sides respectively, depends on both the shape and size of the triangle. It is possible to use the triangle-shape dependence of the bispectrum to measure cosmological parameters like the matter density parameter , and the bias (Hivon et al., 1995, Verde et al., 1998, Matarrese et al., 1997, Taruya et al., 1999, Scoccimarro et al., 1999).