277 research outputs found
Squid Nets of the Mid-Atlantic
This publication illustrates squid nets commonly used along the mid-Atlantic coast
Haunted haloes: tracking the ghosts of subhaloes lost by halo finders
Dark matter subhaloes are key for the predictions of simulations of structure
formation, but their existence frequently ends prematurely due to two technical
issues, namely numerical disruption in N-body simulations and halo finders
failing to identify them. Here we focus on the second issue, using the
phase-space friends-of-friends halo finder ROCKSTAR as a benchmark (though we
expect our results to translate to comparable codes). We confirm that the most
prominent cause for losing track of subhaloes is tidal distortion rather than a
low number of particles. As a solution, we present a flexible post-processing
algorithm that tracks all subhalo particles over time, computes subhalo
positions and masses based on those particles, and progressively removes
stripped matter. If a subhalo is lost by the halo finder, this algorithm keeps
tracking its so-called ghost until it has almost no particles left or has truly
merged with its host. We apply this technique to a large suite of N-body
simulations and restore lost subhaloes to the halo catalogues, which has a
dramatic effect on key summary statistics of large-scale structure.
Specifically, the subhalo mass function increases by about 50% and the halo
correlation function increases by a factor of two at small scales. While these
quantitative results are somewhat specific to our algorithm, they demonstrate
that particle tracking is a promising way to reliably follow haloes and reduce
the need for orphan models. Our algorithm and augmented halo catalogues are
publicly available.Comment: 16 pages, 10 figures. Comments welcom
MultiCAM: A multivariable framework for connecting the mass accretion history of haloes with their properties
Models that connect galaxy and halo properties often summarize a halo's mass
accretion history (MAH) with a single value, and use this value as the basis
for predictions. However, a single-value summary fails to capture the
complexity of MAHs and information can be lost in the process. We present
MultiCAM, a generalization of traditional abundance matching frameworks, which
can simultaneously connect the full MAH of a halo with multiple halo and/or
galaxy properties. As a first case study, we apply MultiCAM to the problem of
connecting dark matter halo properties to their MAHs in the context of a dark
matter-only simulation. While some halo properties, such as concentration, are
more strongly correlated to the early-time mass growth of a halo, others, like
the virial ratio, have stronger correlations with late-time mass growth. This
highlights the necessity of considering the impact of the entire MAH on halo
properties. For most of the halo properties we consider, we find that MultiCAM
models that use the full MAH achieve higher accuracy than conditional abundance
matching models which use a single epoch. We also demonstrate an extension of
MultiCAM that captures the covariance between predicted halo properties. This
extension provides a baseline model for applications where the covariance
between predicted properties is important.Comment: 16 pages, 7 + 1 figures, comments welcome, to be submitted to MNRA
Merger Response of Halo Anisotropy Properties
Anisotropy properties -- halo spin, shape, position offset, velocity offset,
and orientation -- are an important family of dark matter halo properties that
indicate the level of directional variation of the internal structures of
haloes. These properties reflect the dynamical state of haloes, which in turn
depends on the mass assembly history. In this work, we study the evolution of
anisotropy properties in response to merger activity using the IllustrisTNG
simulations. We find that the response trajectories of the anisotropy
properties significantly deviate from secular evolution. These trajectories
have the same qualitative features and timescales across a wide range of merger
and host properties. We propose explanations for the behaviour of these
properties and connect their evolution to the relevant stages of merger
dynamics. We measure the relevant dynamical timescales. We also explore the
dependence of the strength of the response on time of merger, merger ratio, and
mass of the main halo. These results provide insight into the physics of halo
mergers and their effects on the statistical behaviour of halo properties. This
study paves the way towards a physical understanding of scaling relations,
particularly to how systematics in their scatter are connected to the mass
assembly histories of haloes.Comment: 12+3 pages, 5+2 figures. Fig. 4 and 5 are the main figures. To be
submitted to MNRAS, comments welcom
- …