The size and shape dependence of the SDSS galaxy bispectrum

• Published in: New astronomy 2024-12, Vol.113, p.102292, Article 102292
• Main Authors: Nandi, Anindita, Gill, Sukhdeep Singh, Sarkar, Debanjan, Shaw, Abinash Kumar, Pandey, Biswajit, Bharadwaj, Somnath
• Format: Article
• Language: English
• Subjects: Cosmology; Data analysis; Galaxies; Large-scale structure of Universe; Methods; Simulations; Software; Statistics
• ISSN: 1384-1076
• DOI: 10.1016/j.newast.2024.102292

We have measured the spherically averaged bispectrum of the SDSS main galaxy sample, considering a volume-limited [296.75Mpc]3 data cube with mean galaxy number density 0.63×10−3Mpc−3 and median redshift 0.102. Our analysis considers ∼1.37×108 triangles, for which we have measured the binned bispectrum and analysed its dependence on the size and shape of the triangle. It spans wavenumbers k1=(0.075−0.434)Mpc−1 for equilateral triangles, and a smaller range of k1 (the largest side) for triangles of other shapes. For all shapes, we find that the measured bispectrum is well modelled by a power law A(k1/1Mpc−1)n, where the best-fit values of A and n vary with the shape. The parameter A is the minimum for equilateral triangles and increases as the shape is deformed to linear triangles where the two largest sides are nearly aligned, reaching its maximum value for μ=0.95,t=0.75. The values of n are all negative, |n| is minimum (3.12±0.35) for the shape bin μ=0.65,t=0.75, and 3.8±0.28 for μ=0.65,t=0.85. We have also analysed mock galaxy samples constructed from ΛCDM N-body simulations by applying a simple Eulerian bias prescription where the galaxies reside in regions where the smoothed density field exceeds a threshold. We find that the bispectrum from the mock samples with bias b1=1.2 is in good agreement with the SDSS results. We further divided our galaxy sample into red and blue classes and studied the nature of the bispectrum for each category. 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. •We study bispectrum dependence on triangle shapes and sizes in k=0.075−0.434 Mpc-1 .•Bispectrum corresponding to all triangles can be fitted with a single power law.•We visualize the bispectrum corresponding to full triangle-parameter space.•SDSS sample can be modeled with two parameters: smoothing scale and linear bias•Red galaxies exhibit higher bispectrum amplitude than blue ones for all triangles.•Red galaxies are old, and their larger bispectra indicate non-linear interactions•Younger blue galaxies are better tracers of dark matter and, hence, are less biased