Parity-violation

Quijote contains N-body simulations whose intial conditions were generated with parity-violation properties: Quijote-ODD. All these simulations contain \(512^3\) dark matter particles in a periodic volume of \((1~h^{-1}{\rm Gpc})^3\) and share the same cosmology as the fiducial model: \(\Omega_{\rm m}=0.3175\), \(\Omega_{\rm b}=0.049\), \(h=0.6711\), \(n_s=0.9624\), \(\sigma_8=0.834\), \(w=-1\), \(M_\nu=0.0\) eV. As the Quijote-PNG simulations (see Primordial non-Gaussianities), these are standard N-body simulations run with initial conditions generated in a particular way.

The video below shows an example of two N-body simulations with Gaussian initial conditions (top-left) and parity-violating initial conditions (bottom-left). The parity-violating simulation has been flipped along the x-axis to mimick the effect of a mirror in the center. The panels on the right show the differences between both.

Currently, the simulations in Quijote-ODD can be classified into two sets depending on the sign of \(p_{\rm NL}\):

  • ODD_p: 500 simulations with \(p_{\rm NL}=+10^6\).

  • ODD_m: 500 simulations with \(p_{\rm NL}=-10^6\).

The simulations in the above sets can be directly compared (the share the same underlying Gaussian density field) with the first 500 simulations of the fiducial model.

Initial conditions

The initial conditions of the Quijote-ODD simulations have been generated using a modified version of the code described in Scoccimarro et al. 2012. Our modified version of the code is publicly available here.

The initial conditions of a given simulation can be found in a folder called ICs, that contains:

  • ics.X. These are the initial conditions that contain the particle positions, velocities, and IDs. These are Gadget format-II snapshots and can be read as described in Snapshots. X can go from 0 to 127.

  • 2LPT.params. This is the parameter file used to generate the initial conditions.

  • logIC. The output of the initial conditions generator code.

The value of initial random seed for the simulation \(i\) is \(10\times i+5\) (this can be found in the 2LPT.params file) independently of the shape and \(f_{\rm NL}\) value. For instance, the value of the initial random seed for ODD_p/100 and ODD_m/100 is 1005. This choice enables the calculation of partial derivatives, needed for Fisher matrix calculations.

Snapshots

We keep snapshots at redshifts 0, and 1. The snapshots are saved as compressed HDF5 files, and they can be read in the standard way (see Snapshots for details on this).

Halo catalogs

We store both Friends-of-Friends (FoF) and Rockstar halo catalogs for each snapshot of each simulation in Quijote-ODD. We refer the user to Halo catalogs for details on how to read the FoF files. The Rockstar catalogs are ASCII files and the header contains information about the structure of the data.

Density fields

To facilitate the post-processing of the data we also provide 3D grids containing the overdensity, \(\delta(x)=\rho(x)/\bar{\rho}-1\), for each redshift of all PNG simulations. We refer the user to Density fields for details on how to read these files.

Team

Quijote-ODD was developed in 2023 by:

  • William Coulton (CCA, USA)

  • Oliver Philcox (Columbia/Simons, USA)

  • Francisco Villaescusa-Navarro (Simons/Princeton, USA)