SUSSING MERGER TREES: the influence of the halo finder

Abstract

Merger tree codes are routinely used to follow the growth and merger of dark matter haloes in simulations of cosmic structure formation. Whereas in Srisawat et. al. we compared the trees built using a wide variety of such codes here we study the influence of the underlying halo catalogue upon the resulting trees. We observe that the specifics of halo finding itself greatly influences the constructed merger trees. We find that the choices made to define the halo mass are of prime importance. For instance, amongst many potential options different finders select self-bound objects or spherical regions of defined overdensity, decide whether or not to include substructures within the mass returned and vary in their initial particle selection. The impact of these decisions is seen in tree length (the period of time a particularly halo can be traced back through the simulation), branching ratio (essentially the merger rate of subhaloes) and mass evolution. We therefore conclude that the choice of the underlying halo finder is more relevant to the process of building merger trees than the tree builder itself. We also report on some built-in features of specific merger tree codes that (sometimes) help to improve the quality of the merger trees produced.

Exploring the liminality: properties of haloes and subhaloes in borderlinef(R) gravity

“…Such a unique tracking algorithm enables HBT to largely avoid the resolution problem suffered by configuration space subhalo finders (Muldrew, Pearce & Power 2011;Han et al 2012b;Onions et al 2012). By construction, HBT also produces clean and self-consistent merger trees that naturally avoid subtle defects such as missing links and central-satellite swaps common to many other tree builders (Srisawat et al 2013;Avila et al 2014). …”

hbt+: an improved code for finding subhaloes and building merger trees in cosmological simulations

“…Even phase space finders have difficulty dealing with this situation (Behroozi et al 2015). These problems in identifying the main descendant of a merger propagate into the merger tree, giving rise to incorrect or missing links (Han et al 2012;Srisawat et al 2013;Avila et al 2014;.…”

Accurate mass and velocity functions of dark matter haloes

“…From MD emerged the most precise description to date of the dark matter halo . While finding and describing the halos formed by the dark matter is now well understood Knebe et al 2013;Avila et al 2014), connecting galaxies to halos is a proven complicated subject. There are three main streams of galaxy assignment in simulations, we order them by decreasing computational needs and accuracy: (i) hydrodynamical simulations (HYDRO, Cen & Ostriker 1993; comparat@mpe.mpg.de Springel & Hernquist 2003), (ii) semi-analytical models of galaxy formation (SAMS, Cole et al 2000;Baugh 2006), (iii) halo occupation distribution or subhalo abundance matching (HOD, SHAM, Cooray & Sheth 2002;Conroy et al 2006, respectively).…”