Sahyadri: A simulation suite for the cosmology dependence of the Cosmic Web

Abstract

We present Sahyadri, a suite of cosmological $N$-body simulations designed to enable precision studies of the low-redshift Universe with next-generation spectroscopic surveys. Sahyadri includes systematic variations of four cosmological parameters around Planck 2018 constraints, with seed-matched initial conditions enabling cosmological parameter derivatives. It is planned to ultimately extend to six parameters. Each simulation evolves $2048^3$ particles in a periodic box of side length $200$ $h^{-1}$ Mpc, yielding a particle mass of $m_{\mathrm{p}}=8.1\times 10^7{h}^{-1}{M}_{\odot }$ in the fiducial Planck 2018 cosmology. This resolution enables robust identification of dark matter halos down to $M_{\min }=3.2\times 10^9$ $h^{-1}$ $M_{\odot }$, which represents a factor of $\sim$25 improvement over the AbacusSummit suite, and is over two orders of magnitude better than the Quijote and Aemulus suites. We estimate that approximately 40% of DESI BGS galaxies at redshift $z<0.15$ - roughly 1.6 million objects - reside in halos accessible to Sahyadri but beyond the reach of existing parameter-varying simulation suites. We demonstrate Sahyadri's capabilities through measurements of the matter power spectrum, halo mass function and power spectrum, and beyond 2-point statistics such as the Voronoi volume function and $k^{\mathrm{th}}$ nearest neighbour statistics, showing excellent agreement with theoretical predictions and significant sensitivity to $\hat{I}{\text{c◯}}_{\mathrm{m}}$ variations. We implement a custom compression scheme reducing storage requirements by a factor of $\sim$3 while maintaining sub-percent clustering accuracy. Key data products are publicly available.

30 pages, 17 figures. v2: minor changes to match the accepted version; Published in JCAP; DOI 10.1088/1475-7516/2026/07/028; Official Sahyadri website with publicly available data: https://sahyadri.tifr.res.in/index.html

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