Discovering the building blocks of dark matter halo density profiles with neural networks

Abstract

The density profiles of dark matter halos are typically modeled using empirical formulae fitted to the density profiles of relaxed halo populations. We present a neural network model that is trained to learn the mapping from the raw density field containing each halo to the dark matter density profile. We show that the model recovers the widely-used Navarro-Frenk-White (NFW) profile out to the virial radius, and can additionally describe the variability in the outer profile of the halos. The neural network architecture consists of a supervised encoderdecoder framework, which first compresses the density inputs into a low-dimensional latent representation, and then outputs ρ(r) for any desired value of radius r. The latent representation contains all the information used by the model to predict the density profiles. This allows us to interpret the latent representation by quantifying the mutual information between the representation and the halos' ground-truth density profiles. A two-dimensional representation is sufficient to accurately model the density profiles up to the virial radius; however, a threedimensional representation is required to describe the outer profiles beyond the virial radius. The additional dimension in the representation contains information about the infalling material in the outer profiles of dark matter halos, thus discovering the splashback boundary of halos without prior knowledge of the halos' dynamical history.

Insights into the origin of halo mass profiles from machine learning

“…In this work, we adopt a similar framework to assess the importance of the ICs and MAH features in predicting the final mass profile of cluster haloes. Recently, Lucie-Smith et al (2022) extended their work to develop an interpretable deep learning framework to discover the independent set of components required to model the density profiles of dark matter haloes. Here, we focus on a different aspect of dark matter halo profiles: our goal is to improve our understanding of the origin of halo profiles, focusing on how the ICs and haloes' MAH contribute to the build up of the final profiles.…”