Quadratic genetic modifications: a streamlined route to cosmological simulations with controlled merger history

Abstract

Recent work has studied the interplay between a galaxy's history and its\nobservable properties using "genetically modified" cosmological zoom\nsimulations. The approach systematically generates alternative histories for a\nhalo, while keeping its cosmological environment fixed. Applications to date\naltered linear properties of the initial conditions such as the mean\noverdensity of specified regions; we extend the formulation to include\nquadratic features such as local variance, which determines the overall\nimportance of smooth accretion relative to mergers in a galaxy's history. We\nintroduce an efficient algorithm for this new class of modification and\ndemonstrate its ability to control the variance of a region in a\none-dimensional toy model. Outcomes of this work are two-fold: (i) a\nclarification of the formulation of genetic modifications and (ii) a proof of\nconcept for quadratic modifications leading the way to a forthcoming\nimplementation in cosmological simulations.\n