STRAWBERRY: Finding haloes in the gravitational potential

Vol. 707
3. Cosmology (including clusters of galaxies)

STRAWBERRY: Finding haloes in the gravitational potential

Numerical simulations of structure formation in a cosmological context provide an ideal testbed for studying galaxy formation and evolution. Typically, underlying dark matter density is simulated by a number of collisionless particles that only abide by the laws of gravitation. One of the first tasks in analyzing simulation output concerns the detection and identification of halos: bound structures at the center of which galaxies are born. This paper presents a novel algorithm (Strawberry) for identifying such structures, while circumventing the problems associated with standard methods such as friends-of-friends or those that impose spherical symmetry. The authors propose using a potential defined in an accelerated frame – the so-called "boosted potential" – that avoids the arbitrary threshold definition and is defined on a given time snapshot. This potential can be adopted to select the contribution of matter distribution over different scales, so that it can be specifically defined on a smaller structure. The methodology provides an interesting separation of halos into a virialized component and a rapidly evolving one. Figure 3 illustrates the particle assignment, which relies on the turnaround boosted potential definition and iteratively adds particles until another potential valley is found. The code is available in a GitHub repository.