Paicos: A Python package for analysis of (cosmological) simulations performed with Arepo

Cosmological simulations evolve dark matter and baryons subject to gravitational and hydrodynamic forces (Vogelsberger et al., 2020).The simulations start at high redshift and capture hierarchical structure formation where small structures form first and later assemble to larger structures (Springel et al., 2005).The Arepo code is a versatile finite-volume code which can solve the magnetohydrodynamic equations on an unstructured Voronoi mesh in a cosmologically comoving frame (Springel, 2010;Weinberger et al., 2020).Here we present Paicos, a new object-oriented Python package for analyzing simulations performed with Arepo.Paicos strives to reduce the learning curve for students and researchers getting started with Arepo simulations.As such, Paicos includes many examples in the form of Python scripts and Jupyter notebooks (Kluyver et al., 2016) as well as an online documentation describing the installation procedure and recommended first steps.Paicos' main features are automatic handling of cosmological and physical units, computation of derived variables, 2D visualization (slices and projections), 1D and 2D histograms, and easy saving and loading of derived data including units and all the relevant metadata.