How well do integral-of-motion distribution functions describe Milky Way-analogue halos?
Abstract
We study the dark-matter phase space distribution of Milky Way-mass halos in the Auriga simulations, considering both hydrodynamic and dark-matter-only runs. In a spherically averaged potential, we test whether the coarse-grained distribution function can be approximated as a function of the integrals of motion E and L. We find that f(E,L) provides a useful description of the simulated halos: although the deviations from this form are formally statistically significant, the median fractional residuals between radial shells are typically ≲ 15%, with 90th-percentile residuals of order tens of percent. An energy-only approximation, f(E), gives similar median residuals but is systematically disfavored by χ2 tests, indicating that angular momentum dependence is statistically preferred. Ultimately we find that neither f(E) nor f(E,L) fully describes the particle data at high precision. The remaining residuals likely reflect departures from spherical equilibrium, including anisotropy, triaxiality, substructure, and baryonic effects.
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BibTeX
@misc{kumar2026well,
title = {{How well do integral-of-motion distribution functions describe Milky Way-analogue halos?}},
author = {Jason Kumar and Louis E. Strigari},
howpublished = {arXiv},
year = {2026},
month = sep,
doi = {10.48550/arxiv.2609.36283},
eprint = {2609.36283},
archivePrefix = {arXiv},
url = {https://arxiv.org/abs/2609.36283},
}
RIS
TY - UNPB
TI - How well do integral-of-motion distribution functions describe Milky Way-analogue halos?
AU - Jason Kumar
AU - Louis E. Strigari
PY - 2026
DA - 2026/09/28
PB - arXiv
DO - 10.48550/arxiv.2609.36283
UR - https://arxiv.org/abs/2609.36283
AB - We study the dark-matter phase space distribution of Milky Way-mass halos in the Auriga simulations, considering both hydrodynamic and dark-matter-only runs. In a spherically averaged potential, we test whether the coarse-grained distribution function can be approximated as a function of the integrals of motion E and L. We find that f(E,L) provides a useful description of the simulated halos: although the deviations from this form are formally statistically significant, the median fractional residuals between radial shells are typically ≲ 15%, with 90th-percentile residuals of order tens of percent. An energy-only approximation, f(E), gives similar median residuals but is systematically disfavored by χ^2 tests, indicating that angular momentum dependence is statistically preferred. Ultimately we find that neither f(E) nor f(E,L) fully describes the particle data at high precision. The remaining residuals likely reflect departures from spherical equilibrium, including anisotropy, triaxiality, substructure, and baryonic effects.
ER -